three-level timer wheel implementation w/ overflow vector

prep work for s/timing_wheel/tw_timer/ in the vlib process model

Change-Id: I763f4968a8fce1764a3778b12def0afbd30086b1
Signed-off-by: Dave Barach <dave@barachs.net>

12 files changed, 1325 insertions, 77 deletions

diff --git a/src/vppinfra/test_tw_timer.c b/src/vppinfra/test_tw_timer.c
index 26499509..ec0baa07 100644
--- a/src/vppinfra/test_tw_timer.c
+++ b/src/vppinfra/test_tw_timer.c
@@ -3,6 +3,8 @@
 #include <vppinfra/error.h>
 #include <vppinfra/tw_timer_2t_1w_2048sl.h>
 #include <vppinfra/tw_timer_16t_2w_512sl.h>
+#include <vppinfra/tw_timer_4t_3w_256sl.h>
+#include <vppinfra/tw_timer_1t_3w_1024sl_ov.h>
 
 typedef struct
 {
@@ -10,7 +12,7 @@ typedef struct
   u32 stop_timer_handle;
 
   /** Test item should expire at this clock tick */
-  u32 expected_to_expire;
+  u64 expected_to_expire;
 } tw_timer_test_elt_t;
 
 typedef struct
@@ -24,8 +26,14 @@ typedef struct
   /** The double-wheel */
   tw_timer_wheel_16t_2w_512sl_t double_wheel;
 
+  /* The triple wheel */
+  tw_timer_wheel_4t_3w_256sl_t triple_wheel;
+
+  /* The triple wheel with overflow vector */
+  tw_timer_wheel_1t_3w_1024sl_ov_t triple_ov_wheel;
+
   /** random number seed */
-  u32 seed;
+  u64 seed;
 
   /** number of timers */
   u32 ntimers;
@@ -69,6 +77,32 @@ run_double_wheel (tw_timer_wheel_16t_2w_512sl_t * tw, u32 n_ticks)
 }
 
 static void
+run_triple_wheel (tw_timer_wheel_4t_3w_256sl_t * tw, u32 n_ticks)
+{
+  u32 i;
+  f64 now = tw->last_run_time + 1.01;
+
+  for (i = 0; i < n_ticks; i++)
+    {
+      tw_timer_expire_timers_4t_3w_256sl (tw, now);
+      now += 1.01;
+    }
+}
+
+static void
+run_triple_ov_wheel (tw_timer_wheel_1t_3w_1024sl_ov_t * tw, u32 n_ticks)
+{
+  u32 i;
+  f64 now = tw->last_run_time + 1.01;
+
+  for (i = 0; i < n_ticks; i++)
+    {
+      tw_timer_expire_timers_1t_3w_1024sl_ov (tw, now);
+      now += 1.01;
+    }
+}
+
+static void
 expired_timer_single_callback (u32 * expired_timers)
 {
   int i;
@@ -87,7 +121,7 @@ expired_timer_single_callback (u32 * expired_timers)
 
       if (e->expected_to_expire != tm->single_wheel.current_tick)
 	{
-	  fformat (stdout, "[%d] expired at %d not %d\n",
+	  fformat (stdout, "[%d] expired at %lld not %lld\n",
 		   e - tm->test_elts, tm->single_wheel.current_tick,
 		   e->expected_to_expire);
 	}
@@ -114,7 +148,7 @@ expired_timer_double_callback (u32 * expired_timers)
 
       if (e->expected_to_expire != tm->double_wheel.current_tick)
 	{
-	  fformat (stdout, "[%d] expired at %d not %d\n",
+	  fformat (stdout, "[%d] expired at %lld not %lld\n",
 		   e - tm->test_elts, tm->double_wheel.current_tick,
 		   e->expected_to_expire);
 	}
@@ -122,13 +156,64 @@ expired_timer_double_callback (u32 * expired_timers)
     }
 }
 
+static void
+expired_timer_triple_callback (u32 * expired_timers)
+{
+  int i;
+  u32 pool_index, timer_id;
+  tw_timer_test_elt_t *e;
+  tw_timer_test_main_t *tm = &tw_timer_test_main;
+
+  for (i = 0; i < vec_len (expired_timers); i++)
+    {
+      pool_index = expired_timers[i] & 0x3FFFFFFF;
+      timer_id = expired_timers[i] >> 30;
+
+      ASSERT (timer_id == 3);
+
+      e = pool_elt_at_index (tm->test_elts, pool_index);
+
+      if (e->expected_to_expire != tm->triple_wheel.current_tick)
+	{
+	  fformat (stdout, "[%d] expired at %lld not %lld\n",
+		   e - tm->test_elts, tm->triple_wheel.current_tick,
+		   e->expected_to_expire);
+	}
+      pool_put (tm->test_elts, e);
+    }
+}
+
+static void
+expired_timer_triple_ov_callback (u32 * expired_timers)
+{
+  int i;
+  u32 pool_index;
+  tw_timer_test_elt_t *e;
+  tw_timer_test_main_t *tm = &tw_timer_test_main;
+
+  for (i = 0; i < vec_len (expired_timers); i++)
+    {
+      pool_index = expired_timers[i];
+
+      e = pool_elt_at_index (tm->test_elts, pool_index);
+
+      if (e->expected_to_expire != tm->triple_ov_wheel.current_tick)
+	{
+	  fformat (stdout, "[%d] expired at %lld not %lld\n",
+		   e - tm->test_elts, tm->triple_ov_wheel.current_tick,
+		   e->expected_to_expire);
+	}
+      pool_put (tm->test_elts, e);
+    }
+}
+
 static clib_error_t *
 test2_single (tw_timer_test_main_t * tm)
 {
   u32 i, j;
   tw_timer_test_elt_t *e;
   u32 initial_wheel_offset;
-  u32 expiration_time;
+  u64 expiration_time;
   u32 max_expiration_time = 0;
   u32 *deleted_indices = 0;
   u32 adds = 0, deletes = 0;
@@ -145,7 +230,14 @@ test2_single (tw_timer_test_main_t * tm)
 
   run_single_wheel (&tm->single_wheel, initial_wheel_offset);
 
-  fformat (stdout, "test %d timers, %d iter, %d ticks per iter, 0x%x seed\n",
+  fformat (stdout, "initial wheel time %d, fast index %d\n",
+	   tm->single_wheel.current_tick,
+	   tm->single_wheel.current_index[TW_TIMER_RING_FAST]);
+
+  initial_wheel_offset = tm->single_wheel.current_tick;
+
+  fformat (stdout,
+	   "test %d timers, %d iter, %d ticks per iter, 0x%llx seed\n",
 	   tm->ntimers, tm->niter, tm->ticks_per_iter, tm->seed);
 
   before = clib_time_now (&tm->clib_time);
@@ -158,7 +250,7 @@ test2_single (tw_timer_test_main_t * tm)
 
       do
 	{
-	  expiration_time = random_u32 (&tm->seed) & (2047);
+	  expiration_time = random_u64 (&tm->seed) & (2047);
 	}
       while (expiration_time == 0);
 
@@ -192,7 +284,9 @@ test2_single (tw_timer_test_main_t * tm)
 
     del_and_re_add:
       for (j = 0; j < vec_len (deleted_indices); j++)
-	pool_put_index (tm->test_elts, deleted_indices[j]);
+	{
+	  pool_put_index (tm->test_elts, deleted_indices[j]);
+	}
 
       deletes += j;
 
@@ -203,7 +297,7 @@ test2_single (tw_timer_test_main_t * tm)
 
 	  do
 	    {
-	      expiration_time = random_u32 (&tm->seed) & (2047);
+	      expiration_time = random_u64 (&tm->seed) & (2047);
 	    }
 	  while (expiration_time == 0);
 
@@ -269,11 +363,19 @@ test2_double (tw_timer_test_main_t * tm)
 				    1.0 /* timer interval */ , ~0);
 
   /* Prime offset */
-  initial_wheel_offset = 757;
+  initial_wheel_offset = 7577;
 
   run_double_wheel (&tm->double_wheel, initial_wheel_offset);
 
-  fformat (stdout, "test %d timers, %d iter, %d ticks per iter, 0x%x seed\n",
+  fformat (stdout, "initial wheel time %d, fast index %d slow index %d\n",
+	   tm->double_wheel.current_tick,
+	   tm->double_wheel.current_index[TW_TIMER_RING_FAST],
+	   tm->double_wheel.current_index[TW_TIMER_RING_SLOW]);
+
+  initial_wheel_offset = tm->double_wheel.current_tick;
+
+  fformat (stdout,
+	   "test %d timers, %d iter, %d ticks per iter, 0x%llx seed\n",
 	   tm->ntimers, tm->niter, tm->ticks_per_iter, tm->seed);
 
   before = clib_time_now (&tm->clib_time);
@@ -286,7 +388,7 @@ test2_double (tw_timer_test_main_t * tm)
 
       do
 	{
-	  expiration_time = random_u32 (&tm->seed) & ((1 << 17) - 1);
+	  expiration_time = random_u64 (&tm->seed) & ((1 << 17) - 1);
 	}
       while (expiration_time == 0);
 
@@ -294,6 +396,7 @@ test2_double (tw_timer_test_main_t * tm)
 	max_expiration_time = expiration_time;
 
       e->expected_to_expire = expiration_time + initial_wheel_offset;
+
       e->stop_timer_handle =
 	tw_timer_start_16t_2w_512sl (&tm->double_wheel, e - tm->test_elts,
 				     14 /* timer id */ ,
@@ -331,7 +434,7 @@ test2_double (tw_timer_test_main_t * tm)
 
 	  do
 	    {
-	      expiration_time = random_u32 (&tm->seed) & ((1 << 17) - 1);
+	      expiration_time = random_u64 (&tm->seed) & ((1 << 17) - 1);
 	    }
 	  while (expiration_time == 0);
 
@@ -340,6 +443,7 @@ test2_double (tw_timer_test_main_t * tm)
 
 	  e->expected_to_expire = expiration_time +
 	    tm->double_wheel.current_tick;
+
 	  e->stop_timer_handle = tw_timer_start_16t_2w_512sl
 	    (&tm->double_wheel, e - tm->test_elts, 14 /* timer id */ ,
 	     expiration_time);
@@ -379,6 +483,291 @@ test2_double (tw_timer_test_main_t * tm)
 }
 
 static clib_error_t *
+test2_triple (tw_timer_test_main_t * tm)
+{
+  u32 i, j;
+  tw_timer_test_elt_t *e;
+  u32 initial_wheel_offset = 0;
+  u32 expiration_time;
+  u32 max_expiration_time = 0;
+  u32 *deleted_indices = 0;
+  u32 adds = 0, deletes = 0;
+  f64 before, after;
+
+  clib_time_init (&tm->clib_time);
+
+  tw_timer_wheel_init_4t_3w_256sl (&tm->triple_wheel,
+				   expired_timer_triple_callback,
+				   1.0 /* timer interval */ , ~0);
+
+
+  /* Prime offset */
+  initial_wheel_offset = 75700;
+  run_triple_wheel (&tm->triple_wheel, initial_wheel_offset);
+
+  fformat (stdout,
+	   "initial wheel time %d, fi %d si %d gi %d\n",
+	   tm->triple_wheel.current_tick,
+	   tm->triple_wheel.current_index[TW_TIMER_RING_FAST],
+	   tm->triple_wheel.current_index[TW_TIMER_RING_SLOW],
+	   tm->triple_wheel.current_index[TW_TIMER_RING_GLACIER]);
+
+  initial_wheel_offset = tm->triple_wheel.current_tick;
+
+  fformat (stdout,
+	   "test %d timers, %d iter, %d ticks per iter, 0x%llx seed\n",
+	   tm->ntimers, tm->niter, tm->ticks_per_iter, tm->seed);
+
+  before = clib_time_now (&tm->clib_time);
+
+  /* Prime the pump */
+  for (i = 0; i < tm->ntimers; i++)
+    {
+      pool_get (tm->test_elts, e);
+      memset (e, 0, sizeof (*e));
+
+      do
+	{
+	  expiration_time = random_u64 (&tm->seed) & ((1 << 17) - 1);
+	}
+      while (expiration_time == 0);
+
+      if (expiration_time > max_expiration_time)
+	max_expiration_time = expiration_time;
+
+      e->expected_to_expire = expiration_time + initial_wheel_offset;
+
+      e->stop_timer_handle =
+	tw_timer_start_4t_3w_256sl (&tm->triple_wheel, e - tm->test_elts,
+				    3 /* timer id */ ,
+				    expiration_time);
+    }
+
+  adds += i;
+
+  for (i = 0; i < tm->niter; i++)
+    {
+      run_triple_wheel (&tm->triple_wheel, tm->ticks_per_iter);
+
+      j = 0;
+      vec_reset_length (deleted_indices);
+      /* *INDENT-OFF* */
+      pool_foreach (e, tm->test_elts,
+      ({
+        tw_timer_stop_4t_3w_256sl (&tm->triple_wheel, e->stop_timer_handle);
+        vec_add1 (deleted_indices, e - tm->test_elts);
+        if (++j >= tm->ntimers / 4)
+          goto del_and_re_add;
+      }));
+      /* *INDENT-ON* */
+
+    del_and_re_add:
+      for (j = 0; j < vec_len (deleted_indices); j++)
+	pool_put_index (tm->test_elts, deleted_indices[j]);
+
+      deletes += j;
+
+      for (j = 0; j < tm->ntimers / 4; j++)
+	{
+	  pool_get (tm->test_elts, e);
+	  memset (e, 0, sizeof (*e));
+
+	  do
+	    {
+	      expiration_time = random_u64 (&tm->seed) & ((1 << 17) - 1);
+	    }
+	  while (expiration_time == 0);
+
+	  if (expiration_time > max_expiration_time)
+	    max_expiration_time = expiration_time;
+
+	  e->expected_to_expire = expiration_time +
+	    tm->triple_wheel.current_tick;
+
+	  e->stop_timer_handle = tw_timer_start_4t_3w_256sl
+	    (&tm->triple_wheel, e - tm->test_elts, 3 /* timer id */ ,
+	     expiration_time);
+	}
+      adds += j;
+    }
+
+  vec_free (deleted_indices);
+
+  run_triple_wheel (&tm->triple_wheel, max_expiration_time + 1);
+
+  after = clib_time_now (&tm->clib_time);
+
+  fformat (stdout, "%d adds, %d deletes, %d ticks\n", adds, deletes,
+	   tm->triple_wheel.current_tick);
+  fformat (stdout, "test ran %.2f seconds, %.2f ops/second\n",
+	   (after - before),
+	   ((f64) adds + (f64) deletes +
+	    (f64) tm->triple_wheel.current_tick) / (after - before));
+
+  if (pool_elts (tm->test_elts))
+    fformat (stdout, "Note: %d elements remain in pool\n",
+	     pool_elts (tm->test_elts));
+
+  /* *INDENT-OFF* */
+  pool_foreach (e, tm->test_elts,
+  ({
+    fformat (stdout, "[%d] expected to expire %d\n",
+             e - tm->test_elts,
+             e->expected_to_expire);
+  }));
+  /* *INDENT-ON* */
+
+  pool_free (tm->test_elts);
+  tw_timer_wheel_free_4t_3w_256sl (&tm->triple_wheel);
+  return 0;
+}
+
+static clib_error_t *
+test2_triple_ov (tw_timer_test_main_t * tm)
+{
+  u32 i, j;
+  tw_timer_test_elt_t *e;
+  u32 initial_wheel_offset = 0;
+  u32 expiration_time;
+  u32 max_expiration_time = 0;
+  u32 *deleted_indices = 0;
+  u32 adds = 0, deletes = 0;
+  f64 before, after;
+
+  clib_time_init (&tm->clib_time);
+
+  tw_timer_wheel_init_1t_3w_1024sl_ov (&tm->triple_ov_wheel,
+				       expired_timer_triple_ov_callback,
+				       1.0 /* timer interval */ , ~0);
+
+
+  /* Prime offset */
+  initial_wheel_offset = 75700;
+  run_triple_ov_wheel (&tm->triple_ov_wheel, initial_wheel_offset);
+
+  fformat (stdout,
+	   "initial wheel time %d, fi %d si %d gi %d\n",
+	   tm->triple_ov_wheel.current_tick,
+	   tm->triple_ov_wheel.current_index[TW_TIMER_RING_FAST],
+	   tm->triple_ov_wheel.current_index[TW_TIMER_RING_SLOW],
+	   tm->triple_ov_wheel.current_index[TW_TIMER_RING_GLACIER]);
+
+  initial_wheel_offset = tm->triple_ov_wheel.current_tick;
+
+  fformat (stdout,
+	   "test %d timers, %d iter, %d ticks per iter, 0x%llx seed\n",
+	   tm->ntimers, tm->niter, tm->ticks_per_iter, tm->seed);
+
+  before = clib_time_now (&tm->clib_time);
+
+  /* Prime the pump */
+  for (i = 0; i < tm->ntimers; i++)
+    {
+      pool_get (tm->test_elts, e);
+      memset (e, 0, sizeof (*e));
+
+      do
+	{
+	  expiration_time = random_u64 (&tm->seed) & ((1 << 17) - 1);
+	}
+      while (expiration_time == 0);
+
+      if (expiration_time > max_expiration_time)
+	max_expiration_time = expiration_time;
+
+      e->expected_to_expire = expiration_time + initial_wheel_offset;
+
+      e->stop_timer_handle =
+	tw_timer_start_1t_3w_1024sl_ov (&tm->triple_ov_wheel,
+					e - tm->test_elts, 0 /* timer id */ ,
+					expiration_time);
+    }
+
+  adds += i;
+
+  for (i = 0; i < tm->niter; i++)
+    {
+      run_triple_ov_wheel (&tm->triple_ov_wheel, tm->ticks_per_iter);
+
+      j = 0;
+      vec_reset_length (deleted_indices);
+      /* *INDENT-OFF* */
+      pool_foreach (e, tm->test_elts,
+      ({
+        tw_timer_stop_1t_3w_1024sl_ov (&tm->triple_ov_wheel,
+                                       e->stop_timer_handle);
+        vec_add1 (deleted_indices, e - tm->test_elts);
+        if (++j >= tm->ntimers / 4)
+          goto del_and_re_add;
+      }));
+      /* *INDENT-ON* */
+
+    del_and_re_add:
+      for (j = 0; j < vec_len (deleted_indices); j++)
+	pool_put_index (tm->test_elts, deleted_indices[j]);
+
+      deletes += j;
+
+      for (j = 0; j < tm->ntimers / 4; j++)
+	{
+	  pool_get (tm->test_elts, e);
+	  memset (e, 0, sizeof (*e));
+
+	  do
+	    {
+	      expiration_time = random_u64 (&tm->seed) & ((1 << 17) - 1);
+	    }
+	  while (expiration_time == 0);
+
+	  if (expiration_time > max_expiration_time)
+	    max_expiration_time = expiration_time;
+
+	  e->expected_to_expire = expiration_time +
+	    tm->triple_ov_wheel.current_tick;
+
+	  e->stop_timer_handle = tw_timer_start_1t_3w_1024sl_ov
+	    (&tm->triple_ov_wheel, e - tm->test_elts, 0 /* timer id */ ,
+	     expiration_time);
+	}
+      adds += j;
+    }
+
+  vec_free (deleted_indices);
+
+  run_triple_ov_wheel (&tm->triple_ov_wheel, max_expiration_time + 1);
+
+  after = clib_time_now (&tm->clib_time);
+
+  fformat (stdout, "%d adds, %d deletes, %d ticks\n", adds, deletes,
+	   tm->triple_ov_wheel.current_tick);
+  fformat (stdout, "test ran %.2f seconds, %.2f ops/second\n",
+	   (after - before),
+	   ((f64) adds + (f64) deletes +
+	    (f64) tm->triple_ov_wheel.current_tick) / (after - before));
+
+  if (pool_elts (tm->test_elts))
+    fformat (stdout, "Note: %d elements remain in pool\n",
+	     pool_elts (tm->test_elts));
+
+  /* *INDENT-OFF* */
+  pool_foreach (e, tm->test_elts,
+  ({
+    TWT (tw_timer) * t;
+
+    fformat (stdout, "[%d] expected to expire %d\n",
+             e - tm->test_elts,
+             e->expected_to_expire);
+    t = pool_elt_at_index (tm->triple_ov_wheel.timers, e->stop_timer_handle);
+    fformat (stdout, "  expiration_time %lld\n", t->expiration_time);
+  }));
+  /* *INDENT-ON* */
+
+  pool_free (tm->test_elts);
+  tw_timer_wheel_free_1t_3w_1024sl_ov (&tm->triple_ov_wheel);
+  return 0;
+}
+
+static clib_error_t *
 test1_single (tw_timer_test_main_t * tm)
 {
   u32 i;
@@ -401,6 +790,8 @@ test1_single (tw_timer_test_main_t * tm)
 	   tm->single_wheel.current_tick,
 	   tm->single_wheel.current_index[TW_TIMER_RING_FAST]);
 
+  offset = tm->single_wheel.current_tick;
+
   for (i = 0; i < tm->ntimers; i++)
     {
       u32 expected_to_expire;
@@ -504,28 +895,283 @@ test1_double (tw_timer_test_main_t * tm)
 }
 
 static clib_error_t *
+test3_triple_double (tw_timer_test_main_t * tm)
+{
+  tw_timer_test_elt_t *e;
+  u32 initial_wheel_offset = 0;
+  u32 expiration_time;
+  u32 max_expiration_time = 0;
+  u32 adds = 0, deletes = 0;
+  f64 before, after;
+
+  clib_time_init (&tm->clib_time);
+
+  tw_timer_wheel_init_4t_3w_256sl (&tm->triple_wheel,
+				   expired_timer_triple_callback,
+				   1.0 /* timer interval */ , ~0);
+
+  initial_wheel_offset = 0;
+  run_triple_wheel (&tm->triple_wheel, initial_wheel_offset);
+
+  fformat (stdout,
+	   "initial wheel time %d, fi %d si %d gi %d\n",
+	   tm->triple_wheel.current_tick,
+	   tm->triple_wheel.current_index[TW_TIMER_RING_FAST],
+	   tm->triple_wheel.current_index[TW_TIMER_RING_SLOW],
+	   tm->triple_wheel.current_index[TW_TIMER_RING_GLACIER]);
+
+  initial_wheel_offset = tm->triple_wheel.current_tick;
+
+  fformat (stdout, "Create a timer which expires at wheel-time (1, 0, 0)\n");
+
+  before = clib_time_now (&tm->clib_time);
+
+  /* Prime the pump */
+  pool_get (tm->test_elts, e);
+  memset (e, 0, sizeof (*e));
+
+  /* 1 glacier ring tick from now */
+  expiration_time = TW_SLOTS_PER_RING * TW_SLOTS_PER_RING;
+  e->expected_to_expire = expiration_time + initial_wheel_offset;
+  max_expiration_time = expiration_time;
+
+  e->stop_timer_handle =
+    tw_timer_start_4t_3w_256sl (&tm->triple_wheel, e - tm->test_elts,
+				3 /* timer id */ ,
+				expiration_time);
+
+  run_triple_wheel (&tm->triple_wheel, max_expiration_time + 1);
+
+  after = clib_time_now (&tm->clib_time);
+
+  fformat (stdout, "%d adds, %d deletes, %d ticks\n", adds, deletes,
+	   tm->triple_wheel.current_tick);
+  fformat (stdout, "test ran %.2f seconds, %.2f ops/second\n",
+	   (after - before),
+	   ((f64) adds + (f64) deletes +
+	    (f64) tm->triple_wheel.current_tick) / (after - before));
+
+  if (pool_elts (tm->test_elts))
+    fformat (stdout, "Note: %d elements remain in pool\n",
+	     pool_elts (tm->test_elts));
+
+  /* *INDENT-OFF* */
+  pool_foreach (e, tm->test_elts,
+  ({
+    fformat (stdout, "[%d] expected to expire %d\n",
+             e - tm->test_elts,
+             e->expected_to_expire);
+  }));
+  /* *INDENT-ON* */
+
+  pool_free (tm->test_elts);
+  tw_timer_wheel_free_4t_3w_256sl (&tm->triple_wheel);
+  return 0;
+}
+
+static clib_error_t *
+test4_double_double (tw_timer_test_main_t * tm)
+{
+  u32 i;
+  tw_timer_test_elt_t *e;
+  u32 initial_wheel_offset;
+  u32 expiration_time;
+  u32 max_expiration_time = 0;
+  u32 *deleted_indices = 0;
+  u32 adds = 0, deletes = 0;
+  f64 before, after;
+
+  clib_time_init (&tm->clib_time);
+
+  tw_timer_wheel_init_16t_2w_512sl (&tm->double_wheel,
+				    expired_timer_double_callback,
+				    1.0 /* timer interval */ , ~0);
+  /* Prime offset */
+  initial_wheel_offset = 0;
+
+  run_double_wheel (&tm->double_wheel, initial_wheel_offset);
+
+  fformat (stdout, "initial wheel time %d, fast index %d slow index %d\n",
+	   tm->double_wheel.current_tick,
+	   tm->double_wheel.current_index[TW_TIMER_RING_FAST],
+	   tm->double_wheel.current_index[TW_TIMER_RING_SLOW]);
+
+  initial_wheel_offset = tm->double_wheel.current_tick;
+
+  fformat (stdout, "test timer which expires at 512 ticks\n");
+
+  before = clib_time_now (&tm->clib_time);
+
+  /* Prime the pump */
+  for (i = 0; i < tm->ntimers; i++)
+    {
+      pool_get (tm->test_elts, e);
+      memset (e, 0, sizeof (*e));
+
+      expiration_time = 512;
+
+      if (expiration_time > max_expiration_time)
+	max_expiration_time = expiration_time;
+
+      e->expected_to_expire = expiration_time + initial_wheel_offset;
+      e->stop_timer_handle =
+	tw_timer_start_16t_2w_512sl (&tm->double_wheel, e - tm->test_elts,
+				     14 /* timer id */ ,
+				     expiration_time);
+    }
+
+  adds = 1;
+
+  vec_free (deleted_indices);
+
+  run_double_wheel (&tm->double_wheel, max_expiration_time + 1);
+
+  after = clib_time_now (&tm->clib_time);
+
+  fformat (stdout, "%d adds, %d deletes, %d ticks\n", adds, deletes,
+	   tm->double_wheel.current_tick);
+  fformat (stdout, "test ran %.2f seconds, %.2f ops/second\n",
+	   (after - before),
+	   ((f64) adds + (f64) deletes +
+	    (f64) tm->double_wheel.current_tick) / (after - before));
+
+  if (pool_elts (tm->test_elts))
+    fformat (stdout, "Note: %d elements remain in pool\n",
+	     pool_elts (tm->test_elts));
+
+  /* *INDENT-OFF* */
+  pool_foreach (e, tm->test_elts,
+  ({
+    fformat (stdout, "[%d] expected to expire %d\n",
+             e - tm->test_elts,
+             e->expected_to_expire);
+  }));
+  /* *INDENT-ON* */
+
+  pool_free (tm->test_elts);
+  tw_timer_wheel_free_16t_2w_512sl (&tm->double_wheel);
+  return 0;
+}
+
+static clib_error_t *
+test5_double (tw_timer_test_main_t * tm)
+{
+  u32 i;
+  tw_timer_test_elt_t *e;
+  u32 initial_wheel_offset;
+  u32 expiration_time;
+  u32 max_expiration_time = 0;
+  u32 adds = 0, deletes = 0;
+  f64 before, after;
+
+  clib_time_init (&tm->clib_time);
+
+  tw_timer_wheel_init_16t_2w_512sl (&tm->double_wheel,
+				    expired_timer_double_callback,
+				    1.0 /* timer interval */ , ~0);
+
+  /* Prime offset */
+  initial_wheel_offset = 7567;
+
+  run_double_wheel (&tm->double_wheel, initial_wheel_offset);
+
+  fformat (stdout, "initial wheel time %d, fast index %d slow index %d\n",
+	   tm->double_wheel.current_tick,
+	   tm->double_wheel.current_index[TW_TIMER_RING_FAST],
+	   tm->double_wheel.current_index[TW_TIMER_RING_SLOW]);
+
+  initial_wheel_offset = tm->double_wheel.current_tick;
+
+  fformat (stdout,
+	   "test %d timers, %d iter, %d ticks per iter, 0x%llx seed\n",
+	   tm->ntimers, tm->niter, tm->ticks_per_iter, tm->seed);
+
+  before = clib_time_now (&tm->clib_time);
+
+  /* Prime the pump */
+  for (i = 0; i < tm->ntimers; i++)
+    {
+      pool_get (tm->test_elts, e);
+      memset (e, 0, sizeof (*e));
+
+      expiration_time = i + 1;
+
+      if (expiration_time > max_expiration_time)
+	max_expiration_time = expiration_time;
+
+      e->expected_to_expire = expiration_time + initial_wheel_offset;
+      e->stop_timer_handle =
+	tw_timer_start_16t_2w_512sl (&tm->double_wheel, e - tm->test_elts,
+				     14 /* timer id */ ,
+				     expiration_time);
+    }
+
+  adds += i;
+
+  run_double_wheel (&tm->double_wheel, max_expiration_time + 1);
+
+  after = clib_time_now (&tm->clib_time);
+
+  fformat (stdout, "%d adds, %d deletes, %d ticks\n", adds, deletes,
+	   tm->double_wheel.current_tick);
+  fformat (stdout, "test ran %.2f seconds, %.2f ops/second\n",
+	   (after - before),
+	   ((f64) adds + (f64) deletes +
+	    (f64) tm->double_wheel.current_tick) / (after - before));
+
+  if (pool_elts (tm->test_elts))
+    fformat (stdout, "Note: %d elements remain in pool\n",
+	     pool_elts (tm->test_elts));
+
+  /* *INDENT-OFF* */
+  pool_foreach (e, tm->test_elts,
+  ({
+    fformat (stdout, "[%d] expected to expire %d\n",
+             e - tm->test_elts,
+             e->expected_to_expire);
+  }));
+  /* *INDENT-ON* */
+
+  pool_free (tm->test_elts);
+  tw_timer_wheel_free_16t_2w_512sl (&tm->double_wheel);
+  return 0;
+}
+
+static clib_error_t *
 timer_test_command_fn (tw_timer_test_main_t * tm, unformat_input_t * input)
 {
 
   int is_test1 = 0;
   int num_wheels = 1;
   int is_test2 = 0;
+  int is_test3 = 0;
+  int is_test4 = 0;
+  int is_test5 = 0;
+  int overflow = 0;
 
   memset (tm, 0, sizeof (*tm));
   /* Default values */
   tm->ntimers = 100000;
-  tm->seed = 0xDEADDABE;
+  tm->seed = 0xDEADDABEB00BFACE;
   tm->niter = 1000;
   tm->ticks_per_iter = 727;
 
   while (unformat_check_input (input) != UNFORMAT_END_OF_INPUT)
     {
-      if (unformat (input, "seed %d", &tm->seed))
+      if (unformat (input, "seed %lld", &tm->seed))
 	;
       else if (unformat (input, "test1"))
 	is_test1 = 1;
       else if (unformat (input, "test2"))
 	is_test2 = 1;
+      else if (unformat (input, "overflow"))
+	overflow = 1;
+      else if (unformat (input, "lebron"))
+	is_test3 = 1;
+      else if (unformat (input, "wilt"))
+	is_test4 = 1;
+      else if (unformat (input, "linear"))
+	is_test5 = 1;
       else if (unformat (input, "wheels %d", &num_wheels))
 	;
       else if (unformat (input, "ntimers %d", &tm->ntimers))
@@ -534,12 +1180,14 @@ timer_test_command_fn (tw_timer_test_main_t * tm, unformat_input_t * input)
 	;
       else if (unformat (input, "ticks_per_iter %d", &tm->ticks_per_iter))
 	;
+      else
+	break;
     }
 
-  if (is_test1 + is_test2 == 0)
+  if (is_test1 + is_test2 + is_test3 + is_test4 + is_test5 == 0)
     return clib_error_return (0, "No test specified [test1..n]");
 
-  if (num_wheels < 1 || num_wheels > 2)
+  if (num_wheels < 1 || num_wheels > 3)
     return clib_error_return (0, "unsupported... 1 or 2 wheels only");
 
   if (is_test1)
@@ -553,9 +1201,25 @@ timer_test_command_fn (tw_timer_test_main_t * tm, unformat_input_t * input)
     {
       if (num_wheels == 1)
 	return test2_single (tm);
-      else
+      else if (num_wheels == 2)
 	return test2_double (tm);
+      else if (num_wheels == 3)
+	{
+	  if (overflow == 0)
+	    return test2_triple (tm);
+	  else
+	    return test2_triple_ov (tm);
+	}
     }
+  if (is_test3)
+    return test3_triple_double (tm);
+
+  if (is_test4)
+    return test4_double_double (tm);
+
+  if (is_test5)
+    return test5_double (tm);
+
   /* NOTREACHED */
   return 0;
 }
@@ -583,6 +1247,25 @@ main (int argc, char *argv[])
 }
 #endif /* CLIB_UNIX */
 
+/* For debugging... */
+int
+pifi (void *p, u32 index)
+{
+  return pool_is_free_index (p, index);
+}
+
+u32
+vl (void *p)
+{
+  return vec_len (p);
+}
+
+uword
+pe (void *v)
+{
+  return (pool_elts (v));
+}
+
 /*
  * fd.io coding-style-patch-verification: ON
  *
diff --git a/src/vppinfra/tw_timer_16t_1w_2048sl.h b/src/vppinfra/tw_timer_16t_1w_2048sl.h
index 685ac31e..6edef17b 100644
--- a/src/vppinfra/tw_timer_16t_1w_2048sl.h
+++ b/src/vppinfra/tw_timer_16t_1w_2048sl.h
@@ -24,6 +24,7 @@
 #undef TW_TIMERS_PER_OBJECT
 #undef LOG2_TW_TIMERS_PER_OBJECT
 #undef TW_SUFFIX
+#undef TW_OVERFLOW_VECTOR
 
 #define TW_TIMER_WHEELS 1
 #define TW_SLOTS_PER_RING 2048
diff --git a/src/vppinfra/tw_timer_16t_2w_512sl.h b/src/vppinfra/tw_timer_16t_2w_512sl.h
index 93b26d29..2497b31c 100644
--- a/src/vppinfra/tw_timer_16t_2w_512sl.h
+++ b/src/vppinfra/tw_timer_16t_2w_512sl.h
@@ -24,6 +24,7 @@
 #undef TW_TIMERS_PER_OBJECT
 #undef LOG2_TW_TIMERS_PER_OBJECT
 #undef TW_SUFFIX
+#undef TW_OVERFLOW_VECTOR
 
 #define TW_TIMER_WHEELS 2
 #define TW_SLOTS_PER_RING 512
diff --git a/src/vppinfra/tw_timer_1t_3w_1024sl_ov.c b/src/vppinfra/tw_timer_1t_3w_1024sl_ov.c
new file mode 100644
index 00000000..8a65752c
--- /dev/null
+++ b/src/vppinfra/tw_timer_1t_3w_1024sl_ov.c
@@ -0,0 +1,26 @@
+/*
+ * Copyright (c) 2017 Cisco and/or its affiliates.
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at:
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <vppinfra/error.h>
+#include "tw_timer_1t_3w_1024sl_ov.h"
+#include "tw_timer_template.c"
+
+/*
+ * fd.io coding-style-patch-verification: ON
+ *
+ * Local Variables:
+ * eval: (c-set-style "gnu")
+ * End:
+ */
diff --git a/src/vppinfra/tw_timer_1t_3w_1024sl_ov.h b/src/vppinfra/tw_timer_1t_3w_1024sl_ov.h
new file mode 100644
index 00000000..7327f87b
--- /dev/null
+++ b/src/vppinfra/tw_timer_1t_3w_1024sl_ov.h
@@ -0,0 +1,48 @@
+/*
+ * Copyright (c) 2017 Cisco and/or its affiliates.
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at:
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef __included_tw_timer_1t_3w_1024sl_ov_h__
+#define __included_tw_timer_1t_3w_1024sl_ov_h__
+
+/* ... So that a client app can create multiple wheel geometries */
+#undef TW_TIMER_WHEELS
+#undef TW_SLOTS_PER_RING
+#undef TW_RING_SHIFT
+#undef TW_RING_MASK
+#undef TW_TIMERS_PER_OBJECT
+#undef LOG2_TW_TIMERS_PER_OBJECT
+#undef TW_SUFFIX
+#undef TW_OVERFLOW_VECTOR
+
+#define TW_TIMER_WHEELS 3
+#define TW_SLOTS_PER_RING 1024
+#define TW_RING_SHIFT 10
+#define TW_RING_MASK (TW_SLOTS_PER_RING -1)
+#define TW_TIMERS_PER_OBJECT 1
+#define LOG2_TW_TIMERS_PER_OBJECT 0
+#define TW_SUFFIX _1t_3w_1024sl_ov
+#define TW_OVERFLOW_VECTOR 1
+
+#include <vppinfra/tw_timer_template.h>
+
+#endif /* __included_tw_timer_1t_3w_1024sl_ov_h__ */
+
+/*
+ * fd.io coding-style-patch-verification: ON
+ *
+ * Local Variables:
+ * eval: (c-set-style "gnu")
+ * End:
+ */
diff --git a/src/vppinfra/tw_timer_2t_1w_2048sl.h b/src/vppinfra/tw_timer_2t_1w_2048sl.h
index d1cf6d07..33b74405 100644
--- a/src/vppinfra/tw_timer_2t_1w_2048sl.h
+++ b/src/vppinfra/tw_timer_2t_1w_2048sl.h
@@ -24,6 +24,7 @@
 #undef TW_TIMERS_PER_OBJECT
 #undef LOG2_TW_TIMERS_PER_OBJECT
 #undef TW_SUFFIX
+#undef TW_OVERFLOW_VECTOR
 
 #define TW_TIMER_WHEELS 1
 #define TW_SLOTS_PER_RING 2048
diff --git a/src/vppinfra/tw_timer_4t_3w_256sl.c b/src/vppinfra/tw_timer_4t_3w_256sl.c
new file mode 100644
index 00000000..73bb34b2
--- /dev/null
+++ b/src/vppinfra/tw_timer_4t_3w_256sl.c
@@ -0,0 +1,26 @@
+/*
+ * Copyright (c) 2017 Cisco and/or its affiliates.
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at:
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <vppinfra/error.h>
+#include "tw_timer_4t_3w_256sl.h"
+#include "tw_timer_template.c"
+
+/*
+ * fd.io coding-style-patch-verification: ON
+ *
+ * Local Variables:
+ * eval: (c-set-style "gnu")
+ * End:
+ */
diff --git a/src/vppinfra/tw_timer_4t_3w_256sl.h b/src/vppinfra/tw_timer_4t_3w_256sl.h
new file mode 100644
index 00000000..89adb7a2
--- /dev/null
+++ b/src/vppinfra/tw_timer_4t_3w_256sl.h
@@ -0,0 +1,47 @@
+/*
+ * Copyright (c) 2017 Cisco and/or its affiliates.
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at:
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef __included_tw_timer_4t_3w_256sl_h__
+#define __included_tw_timer_4t_3w_256sl_h__
+
+/* ... So that a client app can create multiple wheel geometries */
+#undef TW_TIMER_WHEELS
+#undef TW_SLOTS_PER_RING
+#undef TW_RING_SHIFT
+#undef TW_RING_MASK
+#undef TW_TIMERS_PER_OBJECT
+#undef LOG2_TW_TIMERS_PER_OBJECT
+#undef TW_SUFFIX
+#undef TW_OVERFLOW_VECTOR
+
+#define TW_TIMER_WHEELS 3
+#define TW_SLOTS_PER_RING 256
+#define TW_RING_SHIFT 8
+#define TW_RING_MASK (TW_SLOTS_PER_RING -1)
+#define TW_TIMERS_PER_OBJECT 4
+#define LOG2_TW_TIMERS_PER_OBJECT 2
+#define TW_SUFFIX _4t_3w_256sl
+
+#include <vppinfra/tw_timer_template.h>
+
+#endif /* __included_tw_timer_4t_3w_256sl_h__ */
+
+/*
+ * fd.io coding-style-patch-verification: ON
+ *
+ * Local Variables:
+ * eval: (c-set-style "gnu")
+ * End:
+ */
diff --git a/src/vppinfra/tw_timer_4t_3w_4sl_ov.c b/src/vppinfra/tw_timer_4t_3w_4sl_ov.c
new file mode 100644
index 00000000..e2af7b5d
--- /dev/null
+++ b/src/vppinfra/tw_timer_4t_3w_4sl_ov.c
@@ -0,0 +1,32 @@
+/*
+ * Copyright (c) 2017 Cisco and/or its affiliates.
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at:
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/*
+ * This wheel geometry is not prima facie useful, except for testing
+ */
+
+#if TW_TIMER_TEST_GEOMETRY > 0
+#include <vppinfra/error.h>
+#include "tw_timer_4t_3w_4sl_ov.h"
+#include "tw_timer_template.c"
+#endif
+
+/*
+ * fd.io coding-style-patch-verification: ON
+ *
+ * Local Variables:
+ * eval: (c-set-style "gnu")
+ * End:
+ */
diff --git a/src/vppinfra/tw_timer_4t_3w_4sl_ov.h b/src/vppinfra/tw_timer_4t_3w_4sl_ov.h
new file mode 100644
index 00000000..0f76164d
--- /dev/null
+++ b/src/vppinfra/tw_timer_4t_3w_4sl_ov.h
@@ -0,0 +1,48 @@
+/*
+ * Copyright (c) 2017 Cisco and/or its affiliates.
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at:
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef __included_tw_timer_4t_3w_4sl_ov_h__
+#define __included_tw_timer_4t_3w_4sl_ov_h__
+
+/* ... So that a client app can create multiple wheel geometries */
+#undef TW_TIMER_WHEELS
+#undef TW_SLOTS_PER_RING
+#undef TW_RING_SHIFT
+#undef TW_RING_MASK
+#undef TW_TIMERS_PER_OBJECT
+#undef LOG2_TW_TIMERS_PER_OBJECT
+#undef TW_SUFFIX
+#undef TW_OVERFLOW_VECTOR
+
+#define TW_TIMER_WHEELS 3
+#define TW_SLOTS_PER_RING 4
+#define TW_RING_SHIFT 2
+#define TW_RING_MASK (TW_SLOTS_PER_RING -1)
+#define TW_TIMERS_PER_OBJECT 4
+#define LOG2_TW_TIMERS_PER_OBJECT 2
+#define TW_SUFFIX _4t_3w_4sl_ov
+#define TW_OVERFLOW_VECTOR 1
+
+#include <vppinfra/tw_timer_template.h>
+
+#endif /* __included_tw_timer_4t_3w_256sl_h__ */
+
+/*
+ * fd.io coding-style-patch-verification: ON
+ *
+ * Local Variables:
+ * eval: (c-set-style "gnu")
+ * End:
+ */
diff --git a/src/vppinfra/tw_timer_template.c b/src/vppinfra/tw_timer_template.c
index e3f44500..a0c407ae 100644
--- a/src/vppinfra/tw_timer_template.c
+++ b/src/vppinfra/tw_timer_template.c
@@ -18,16 +18,19 @@
  *
  *
  */
-
 static inline u32
 TW (make_internal_timer_handle) (u32 pool_index, u32 timer_id)
 {
   u32 handle;
 
   ASSERT (timer_id < TW_TIMERS_PER_OBJECT);
+#if LOG2_TW_TIMERS_PER_OBJECT > 0
   ASSERT (pool_index < (1 << (32 - LOG2_TW_TIMERS_PER_OBJECT)));
 
   handle = (timer_id << (32 - LOG2_TW_TIMERS_PER_OBJECT)) | (pool_index);
+#else
+  handle = pool_index;
+#endif
   return handle;
 }
 
@@ -79,17 +82,23 @@ timer_remove (TWT (tw_timer) * pool, u32 index)
  * @param tw_timer_wheel_t * tw timer wheel object pointer
  * @param u32 pool_index user pool index, presumably for a tw session
  * @param u32 timer_id app-specific timer ID. 4 bits.
- * @param u32 interval timer interval in ticks
+ * @param u64 interval timer interval in ticks
  * @returns handle needed to cancel the timer
  */
 u32
 TW (tw_timer_start) (TWT (tw_timer_wheel) * tw, u32 pool_index, u32 timer_id,
-		     u32 interval)
+		     u64 interval)
 {
 #if TW_TIMER_WHEELS > 1
   u16 slow_ring_offset;
   u32 carry;
 #endif
+#if TW_TIMER_WHEELS > 2
+  u16 glacier_ring_offset;
+#endif
+#if TW_OVERFLOW_VECTOR > 0
+  u64 interval_plus_time_to_wrap, triple_wrap_mask;
+#endif
   u16 fast_ring_offset;
   tw_timer_wheel_slot_t *ts;
   TWT (tw_timer) * t;
@@ -97,31 +106,89 @@ TW (tw_timer_start) (TWT (tw_timer_wheel) * tw, u32 pool_index, u32 timer_id,
   ASSERT (interval);
 
   pool_get (tw->timers, t);
-  t->next = t->prev = ~0;
-#if TW_TIMER_WHEELS > 1
-  t->fast_ring_offset = ~0;
-#endif
+  memset (t, 0xff, sizeof (*t));
+
   t->user_handle = TW (make_internal_timer_handle) (pool_index, timer_id);
 
+  /* Factor interval into 1..3 wheel offsets */
+#if TW_TIMER_WHEELS > 2
+#if TW_OVERFLOW_VECTOR > 0
+  /*
+   * This is tricky. Put a timer onto the overflow
+   * vector if the interval PLUS the time
+   * until the next triple-wrap exceeds one full revolution
+   * of all three wheels.
+   */
+  triple_wrap_mask = (1 << (3 * TW_RING_SHIFT)) - 1;
+  interval_plus_time_to_wrap =
+    interval + (tw->current_tick & triple_wrap_mask);
+  if ((interval_plus_time_to_wrap >= 1 << (3 * TW_RING_SHIFT)))
+    {
+      t->expiration_time = tw->current_tick + interval;
+      ts = &tw->overflow;
+      timer_addhead (tw->timers, ts->head_index, t - tw->timers);
+      return t - tw->timers;
+    }
+#endif
+
+  glacier_ring_offset = interval >> (2 * TW_RING_SHIFT);
+  ASSERT (glacier_ring_offset < TW_SLOTS_PER_RING);
+  interval -= (glacier_ring_offset << (2 * TW_RING_SHIFT));
+#endif
+#if TW_TIMER_WHEELS > 1
+  slow_ring_offset = interval >> TW_RING_SHIFT;
+  ASSERT (slow_ring_offset < TW_SLOTS_PER_RING);
+  interval -= (slow_ring_offset << TW_RING_SHIFT);
+#endif
   fast_ring_offset = interval & TW_RING_MASK;
-  fast_ring_offset += tw->current_index[TW_TIMER_RING_FAST];
+
+  /*
+   * Account for the current wheel positions(s)
+   * This is made slightly complicated by the fact that the current
+   * index vector will contain (TW_SLOTS_PER_RING, ...) when
+   * the actual position is (0, ...)
+   */
+
+  fast_ring_offset += tw->current_index[TW_TIMER_RING_FAST] & TW_RING_MASK;
+
 #if TW_TIMER_WHEELS > 1
   carry = fast_ring_offset >= TW_SLOTS_PER_RING ? 1 : 0;
   fast_ring_offset %= TW_SLOTS_PER_RING;
-  slow_ring_offset = (interval >> TW_RING_SHIFT) + carry;
+  slow_ring_offset += (tw->current_index[TW_TIMER_RING_SLOW] & TW_RING_MASK)
+    + carry;
+  carry = slow_ring_offset >= TW_SLOTS_PER_RING ? 1 : 0;
+  slow_ring_offset %= TW_SLOTS_PER_RING;
+#endif
 
-  /* Timer duration exceeds ~7 hrs? Oops */
-  ASSERT (slow_ring_offset < TW_SLOTS_PER_RING);
+#if TW_TIMER_WHEELS > 2
+  glacier_ring_offset +=
+    (tw->current_index[TW_TIMER_RING_GLACIER] & TW_RING_MASK) + carry;
+  glacier_ring_offset %= TW_SLOTS_PER_RING;
+#endif
 
-  /* Timer expires more than 51.2 seconds from now? */
-  if (slow_ring_offset)
+#if TW_TIMER_WHEELS > 2
+  if (glacier_ring_offset !=
+      (tw->current_index[TW_TIMER_RING_GLACIER] & TW_RING_MASK))
     {
-      slow_ring_offset += tw->current_index[TW_TIMER_RING_SLOW];
-      slow_ring_offset %= TW_SLOTS_PER_RING;
+      /* We'll need slow and fast ring offsets later */
+      t->slow_ring_offset = slow_ring_offset;
+      t->fast_ring_offset = fast_ring_offset;
 
-      /* We'll want the fast ring offset later... */
+      ts = &tw->w[TW_TIMER_RING_GLACIER][glacier_ring_offset];
+
+      timer_addhead (tw->timers, ts->head_index, t - tw->timers);
+
+      return t - tw->timers;
+    }
+#endif
+
+#if TW_TIMER_WHEELS > 1
+  /* Timer expires more than 51.2 seconds from now? */
+  if (slow_ring_offset !=
+      (tw->current_index[TW_TIMER_RING_SLOW] & TW_RING_MASK))
+    {
+      /* We'll need the fast ring offset later... */
       t->fast_ring_offset = fast_ring_offset;
-      ASSERT (t->fast_ring_offset < TW_SLOTS_PER_RING);
 
       ts = &tw->w[TW_TIMER_RING_SLOW][slow_ring_offset];
 
@@ -131,7 +198,6 @@ TW (tw_timer_start) (TWT (tw_timer_wheel) * tw, u32 pool_index, u32 timer_id,
     }
 #else
   fast_ring_offset %= TW_SLOTS_PER_RING;
-  ASSERT (interval < TW_SLOTS_PER_RING);
 #endif
 
   /* Timer expires less than one fast-ring revolution from now */
@@ -141,6 +207,41 @@ TW (tw_timer_start) (TWT (tw_timer_wheel) * tw, u32 pool_index, u32 timer_id,
   return t - tw->timers;
 }
 
+#if TW_TIMER_SCAN_FOR_HANDLE > 0
+int TW (scan_for_handle) (TWT (tw_timer_wheel) * tw, u32 handle)
+{
+  int i, j;
+  tw_timer_wheel_slot_t *ts;
+  TWT (tw_timer) * t, *head;
+  u32 next_index;
+  int rv = 0;
+
+  for (i = 0; i < TW_TIMER_WHEELS; i++)
+    {
+      for (j = 0; j < TW_SLOTS_PER_RING; j++)
+	{
+	  ts = &tw->w[i][j];
+	  head = pool_elt_at_index (tw->timers, ts->head_index);
+	  next_index = head->next;
+
+	  while (next_index != ts->head_index)
+	    {
+	      t = pool_elt_at_index (tw->timers, next_index);
+	      if (next_index == handle)
+		{
+		  clib_warning ("handle %d found in ring %d slot %d",
+				handle, i, j);
+		  clib_warning ("user handle 0x%x", t->user_handle);
+		  rv = 1;
+		}
+	      next_index = t->next;
+	    }
+	}
+    }
+  return rv;
+}
+#endif /* TW_TIMER_SCAN_FOR_HANDLE */
+
 /**
  * @brief Stop a tw timer
  * @param tw_timer_wheel_t * tw timer wheel object pointer
@@ -164,7 +265,7 @@ void TW (tw_timer_stop) (TWT (tw_timer_wheel) * tw, u32 handle)
  * @brief Initialize a tw timer wheel template instance
  * @param tw_timer_wheel_t * tw timer wheel object pointer
  * @param void * expired_timer_callback. Passed a u32 * vector of
- *   expired timer handles.
+ *   expired timer handles. The callback is optional.
  * @param f64 timer_interval_in_seconds
  */
 void
@@ -185,6 +286,9 @@ TW (tw_timer_wheel_init) (TWT (tw_timer_wheel) * tw,
     }
   tw->timer_interval = timer_interval_in_seconds;
   tw->ticks_per_second = 1.0 / timer_interval_in_seconds;
+  tw->first_expires_tick = ~0ULL;
+  vec_validate (tw->expired_timer_handles, 0);
+  _vec_len (tw->expired_timer_handles) = 0;
 
   for (ring = 0; ring < TW_TIMER_WHEELS; ring++)
     {
@@ -197,6 +301,14 @@ TW (tw_timer_wheel_init) (TWT (tw_timer_wheel) * tw,
 	  ts->head_index = t - tw->timers;
 	}
     }
+
+#if TW_OVERFLOW_VECTOR > 0
+  ts = &tw->overflow;
+  pool_get (tw->timers, t);
+  memset (t, 0xff, sizeof (*t));
+  t->next = t->prev = t - tw->timers;
+  ts->head_index = t - tw->timers;
+#endif
 }
 
 /**
@@ -227,6 +339,21 @@ void TW (tw_timer_wheel_free) (TWT (tw_timer_wheel) * tw)
 	  pool_put (tw->timers, head);
 	}
     }
+
+#if TW_OVERFLOW_VECVOR > 0
+  ts = &tw->overflow;
+  head = pool_elt_at_index (tw->timers, ts->head_index);
+  next_index = head->next;
+
+  while (next_index != ts->head_index)
+    {
+      t = pool_elt_at_index (tw->timers, next_index);
+      next_index = t->next;
+      pool_put (tw->timers, t);
+    }
+  pool_put (tw->timers, head);
+#endif
+
   memset (tw, 0, sizeof (*tw));
 }
 
@@ -235,50 +362,185 @@ void TW (tw_timer_wheel_free) (TWT (tw_timer_wheel) * tw)
  * as needed. This routine should be called once every timer_interval seconds
  * @param tw_timer_wheel_t * tw timer wheel template instance pointer
  * @param f64 now the current time, e.g. from vlib_time_now(vm)
+ * @returns u32 * vector of expired user handles
  */
-u32 TW (tw_timer_expire_timers) (TWT (tw_timer_wheel) * tw, f64 now)
+static inline
+  u32 * TW (tw_timer_expire_timers_internal) (TWT (tw_timer_wheel) * tw,
+					      f64 now,
+					      u32 * callback_vector_arg)
 {
   u32 nticks, i;
   tw_timer_wheel_slot_t *ts;
   TWT (tw_timer) * t, *head;
+  u32 *callback_vector;
   u32 fast_wheel_index;
   u32 next_index;
-  u32 nexpirations, total_nexpirations;
-#if TW_TIMER_WHEELS > 1
-  u32 slow_wheel_index;
-#endif
+  u32 slow_wheel_index __attribute__ ((unused));
+  u32 glacier_wheel_index __attribute__ ((unused));
 
   /* Shouldn't happen */
   if (PREDICT_FALSE (now < tw->next_run_time))
-    return 0;
+    return callback_vector_arg;
 
   /* Number of ticks which have occurred */
   nticks = tw->ticks_per_second * (now - tw->last_run_time);
   if (nticks == 0)
-    return 0;
+    return callback_vector_arg;
 
   /* Remember when we ran, compute next runtime */
   tw->next_run_time = (now + tw->timer_interval);
 
-  total_nexpirations = 0;
+  if (callback_vector_arg == 0)
+    {
+      _vec_len (tw->expired_timer_handles) = 0;
+      callback_vector = tw->expired_timer_handles;
+    }
+  else
+    callback_vector = callback_vector_arg;
+
   for (i = 0; i < nticks; i++)
     {
       fast_wheel_index = tw->current_index[TW_TIMER_RING_FAST];
+      if (TW_TIMER_WHEELS > 1)
+	slow_wheel_index = tw->current_index[TW_TIMER_RING_SLOW];
+      if (TW_TIMER_WHEELS > 2)
+	glacier_wheel_index = tw->current_index[TW_TIMER_RING_GLACIER];
+
+#if TW_OVERFLOW_VECTOR > 0
+      /* Triple odometer-click? Process the overflow vector... */
+      if (PREDICT_FALSE (fast_wheel_index == TW_SLOTS_PER_RING
+			 && slow_wheel_index == TW_SLOTS_PER_RING
+			 && glacier_wheel_index == TW_SLOTS_PER_RING))
+	{
+	  u64 interval;
+	  u32 new_glacier_ring_offset, new_slow_ring_offset;
+	  u32 new_fast_ring_offset;
 
+	  ts = &tw->overflow;
+	  head = pool_elt_at_index (tw->timers, ts->head_index);
+	  next_index = head->next;
+
+	  /* Make slot empty */
+	  head->next = head->prev = ts->head_index;
+
+	  /* traverse slot, place timers wherever they go */
+	  while (next_index != head - tw->timers)
+	    {
+	      t = pool_elt_at_index (tw->timers, next_index);
+	      next_index = t->next;
+
+	      /* Remove from the overflow vector (hammer) */
+	      t->next = t->prev = ~0;
+
+	      ASSERT (t->expiration_time >= tw->current_tick);
+
+	      interval = t->expiration_time - tw->current_tick;
+
+	      /* Right back onto the overflow vector? */
+	      if (interval >= (1 << (3 * TW_RING_SHIFT)))
+		{
+		  ts = &tw->overflow;
+		  timer_addhead (tw->timers, ts->head_index, t - tw->timers);
+		  continue;
+		}
+	      /* Compute ring offsets */
+	      new_glacier_ring_offset = interval >> (2 * TW_RING_SHIFT);
+
+	      interval -= (new_glacier_ring_offset << (2 * TW_RING_SHIFT));
+
+	      /* Note: the wheels are at (0,0,0), no add-with-carry needed */
+	      new_slow_ring_offset = interval >> TW_RING_SHIFT;
+	      interval -= (new_slow_ring_offset << TW_RING_SHIFT);
+	      new_fast_ring_offset = interval & TW_RING_MASK;
+	      t->slow_ring_offset = new_slow_ring_offset;
+	      t->fast_ring_offset = new_fast_ring_offset;
+
+	      /* Timer expires Right Now */
+	      if (PREDICT_FALSE (t->slow_ring_offset == 0 &&
+				 t->fast_ring_offset == 0 &&
+				 new_glacier_ring_offset == 0))
+		{
+		  vec_add1 (callback_vector, t->user_handle);
+		  pool_put (tw->timers, t);
+		}
+	      /* Timer moves to the glacier ring */
+	      else if (new_glacier_ring_offset)
+		{
+		  ts = &tw->w[TW_TIMER_RING_GLACIER][new_glacier_ring_offset];
+		  timer_addhead (tw->timers, ts->head_index, t - tw->timers);
+		}
+	      /* Timer moves to the slow ring */
+	      else if (t->slow_ring_offset)
+		{
+		  /* Add to slow ring */
+		  ts = &tw->w[TW_TIMER_RING_SLOW][t->slow_ring_offset];
+		  timer_addhead (tw->timers, ts->head_index, t - tw->timers);
+		}
+	      /* Timer timer moves to the fast ring */
+	      else
+		{
+		  ts = &tw->w[TW_TIMER_RING_FAST][t->fast_ring_offset];
+		  timer_addhead (tw->timers, ts->head_index, t - tw->timers);
+		}
+	    }
+	}
+#endif
+
+#if TW_TIMER_WHEELS > 2
       /*
-       * If we've been around the fast ring once,
-       * process one slot in the slow ring before we handle
-       * the fast ring.
+       * Double odometer-click? Process one slot in the glacier ring...
        */
-      if (PREDICT_FALSE (fast_wheel_index == TW_SLOTS_PER_RING))
+      if (PREDICT_FALSE (fast_wheel_index == TW_SLOTS_PER_RING
+			 && slow_wheel_index == TW_SLOTS_PER_RING))
 	{
-	  fast_wheel_index = tw->current_index[TW_TIMER_RING_FAST] = 0;
+	  glacier_wheel_index %= TW_SLOTS_PER_RING;
+	  ts = &tw->w[TW_TIMER_RING_GLACIER][glacier_wheel_index];
 
-#if TW_TIMER_WHEELS > 1
-	  tw->current_index[TW_TIMER_RING_SLOW]++;
-	  tw->current_index[TW_TIMER_RING_SLOW] %= TW_SLOTS_PER_RING;
-	  slow_wheel_index = tw->current_index[TW_TIMER_RING_SLOW];
+	  head = pool_elt_at_index (tw->timers, ts->head_index);
+	  next_index = head->next;
+
+	  /* Make slot empty */
+	  head->next = head->prev = ts->head_index;
+
+	  /* traverse slot, deal timers into slow ring */
+	  while (next_index != head - tw->timers)
+	    {
+	      t = pool_elt_at_index (tw->timers, next_index);
+	      next_index = t->next;
+
+	      /* Remove from glacier ring slot (hammer) */
+	      t->next = t->prev = ~0;
+
+	      /* Timer expires Right Now */
+	      if (PREDICT_FALSE (t->slow_ring_offset == 0 &&
+				 t->fast_ring_offset == 0))
+		{
+		  vec_add1 (callback_vector, t->user_handle);
+		  pool_put (tw->timers, t);
+		}
+	      /* Timer expires during slow-wheel tick 0 */
+	      else if (PREDICT_FALSE (t->slow_ring_offset == 0))
+		{
+		  ts = &tw->w[TW_TIMER_RING_FAST][t->fast_ring_offset];
+		  timer_addhead (tw->timers, ts->head_index, t - tw->timers);
+		}
+	      else		/* typical case */
+		{
+		  /* Add to slow ring */
+		  ts = &tw->w[TW_TIMER_RING_SLOW][t->slow_ring_offset];
+		  timer_addhead (tw->timers, ts->head_index, t - tw->timers);
+		}
+	    }
+	}
+#endif
 
+#if TW_TIMER_WHEELS > 1
+      /*
+       * Single odometer-click? Process a slot in the slow ring,
+       */
+      if (PREDICT_FALSE (fast_wheel_index == TW_SLOTS_PER_RING))
+	{
+	  slow_wheel_index %= TW_SLOTS_PER_RING;
 	  ts = &tw->w[TW_TIMER_RING_SLOW][slow_wheel_index];
 
 	  head = pool_elt_at_index (tw->timers, ts->head_index);
@@ -293,19 +555,27 @@ u32 TW (tw_timer_expire_timers) (TWT (tw_timer_wheel) * tw, f64 now)
 	      t = pool_elt_at_index (tw->timers, next_index);
 	      next_index = t->next;
 
-	      /* Remove from slow ring slot (hammer) */
+	      /* Remove from sloe ring slot (hammer) */
 	      t->next = t->prev = ~0;
-	      ASSERT (t->fast_ring_offset < TW_SLOTS_PER_RING);
-	      /* Add to fast ring */
-	      ts = &tw->w[TW_TIMER_RING_FAST][t->fast_ring_offset];
-	      timer_addhead (tw->timers, ts->head_index, t - tw->timers);
+
+	      /* Timer expires Right Now */
+	      if (PREDICT_FALSE (t->fast_ring_offset == 0))
+		{
+		  vec_add1 (callback_vector, t->user_handle);
+		  pool_put (tw->timers, t);
+		}
+	      else		/* typical case */
+		{
+		  /* Add to fast ring */
+		  ts = &tw->w[TW_TIMER_RING_FAST][t->fast_ring_offset];
+		  timer_addhead (tw->timers, ts->head_index, t - tw->timers);
+		}
 	    }
-#endif
 	}
+#endif
 
       /* Handle the fast ring */
-      vec_reset_length (tw->expired_timer_handles);
-
+      fast_wheel_index %= TW_SLOTS_PER_RING;
       ts = &tw->w[TW_TIMER_RING_FAST][fast_wheel_index];
 
       head = pool_elt_at_index (tw->timers, ts->head_index);
@@ -319,26 +589,57 @@ u32 TW (tw_timer_expire_timers) (TWT (tw_timer_wheel) * tw, f64 now)
 	{
 	  t = pool_elt_at_index (tw->timers, next_index);
 	  next_index = t->next;
-	  vec_add1 (tw->expired_timer_handles, t->user_handle);
+	  vec_add1 (callback_vector, t->user_handle);
 	  pool_put (tw->timers, t);
 	}
 
       /* If any timers expired, tell the user */
-      nexpirations = vec_len (tw->expired_timer_handles);
-      if (nexpirations)
+      if (callback_vector_arg == 0 && vec_len (callback_vector))
 	{
-	  tw->expired_timer_callback (tw->expired_timer_handles);
-	  total_nexpirations += nexpirations;
+	  /* The callback is optional. We return the u32 * handle vector */
+	  if (tw->expired_timer_callback)
+	    {
+	      tw->expired_timer_callback (callback_vector);
+	      _vec_len (callback_vector) = 0;
+	    }
+	  tw->expired_timer_handles = callback_vector;
 	}
-      tw->current_index[TW_TIMER_RING_FAST]++;
       tw->current_tick++;
+      fast_wheel_index++;
+      tw->current_index[TW_TIMER_RING_FAST] = fast_wheel_index;
+
+#if TW_TIMER_WHEELS > 1
+      if (PREDICT_FALSE (fast_wheel_index == TW_SLOTS_PER_RING))
+	slow_wheel_index++;
+      tw->current_index[TW_TIMER_RING_SLOW] = slow_wheel_index;
+#endif
+
+#if TW_TIMER_WHEELS > 2
+      if (PREDICT_FALSE (slow_wheel_index == TW_SLOTS_PER_RING))
+	glacier_wheel_index++;
+      tw->current_index[TW_TIMER_RING_GLACIER] = glacier_wheel_index;
+#endif
 
-      if (total_nexpirations >= tw->max_expirations)
+      if (vec_len (callback_vector) >= tw->max_expirations)
 	break;
     }
 
+  if (callback_vector_arg == 0)
+    tw->expired_timer_handles = callback_vector;
+
   tw->last_run_time += i * tw->timer_interval;
-  return total_nexpirations;
+  return callback_vector;
+}
+
+u32 *TW (tw_timer_expire_timers) (TWT (tw_timer_wheel) * tw, f64 now)
+{
+  return TW (tw_timer_expire_timers_internal) (tw, now, 0 /* no vector */ );
+}
+
+u32 *TW (tw_timer_expire_timers_vec) (TWT (tw_timer_wheel) * tw, f64 now,
+				      u32 * vec)
+{
+  return TW (tw_timer_expire_timers_internal) (tw, now, vec);
 }
 
 /*
diff --git a/src/vppinfra/tw_timer_template.h b/src/vppinfra/tw_timer_template.h
index 6b61e424..76755609 100644
--- a/src/vppinfra/tw_timer_template.h
+++ b/src/vppinfra/tw_timer_template.h
@@ -110,16 +110,39 @@ Expired timer callback:
      }
  */
 
+#if (TW_TIMER_WHEELS != 1 && TW_TIMER_WHEELS != 2 && TW_TIMER_WHEELS != 3)
+#error TW_TIMER_WHEELS must be 1, 2 or 3
+#endif
+
 typedef struct
 {
   /** next, previous pool indices */
   u32 next;
   u32 prev;
-#if TW_TIMER_WHEELS > 0
-  /** fast ring offset, only valid in the slow ring */
-  u16 fast_ring_offset;
-  u16 pad;
+
+  union
+  {
+    struct
+    {
+#if (TW_TIMER_WHEELS == 3)
+      /** fast ring offset, only valid in the slow ring */
+      u16 fast_ring_offset;
+      /** slow ring offset, only valid in the glacier ring */
+      u16 slow_ring_offset;
+#endif
+#if (TW_TIMER_WHEELS == 2)
+      /** fast ring offset, only valid in the slow ring */
+      u16 fast_ring_offset;
+      /** slow ring offset, only valid in the glacier ring */
+      u16 pad;
 #endif
+    };
+
+#if (TW_OVERFLOW_VECTOR > 0)
+    u64 expiration_time;
+#endif
+  };
+
   /** user timer handle */
   u32 user_handle;
 } TWT (tw_timer);
@@ -141,6 +164,8 @@ typedef enum
   TW_TIMER_RING_FAST,
   /** Slow timer ring ID */
   TW_TIMER_RING_SLOW,
+  /** Glacier ring ID */
+  TW_TIMER_RING_GLACIER,
 } tw_ring_index_t;
 #endif /* __defined_tw_timer_wheel_slot__ */
 
@@ -162,7 +187,10 @@ typedef struct
   f64 timer_interval;
 
   /** current tick */
-  u32 current_tick;
+  u64 current_tick;
+
+  /** first expiration time */
+  u64 first_expires_tick;
 
   /** current wheel indices */
   u32 current_index[TW_TIMER_WHEELS];
@@ -170,6 +198,10 @@ typedef struct
   /** wheel arrays */
   tw_timer_wheel_slot_t w[TW_TIMER_WHEELS][TW_SLOTS_PER_RING];
 
+#if TW_OVERFLOW_VECTOR > 0
+  tw_timer_wheel_slot_t overflow;
+#endif
+
   /** expired timer callback, receives a vector of handles */
   void (*expired_timer_callback) (u32 * expired_timer_handles);
 
@@ -181,7 +213,7 @@ typedef struct
 } TWT (tw_timer_wheel);
 
 u32 TW (tw_timer_start) (TWT (tw_timer_wheel) * tw,
-			 u32 pool_index, u32 timer_id, u32 interval);
+			 u32 pool_index, u32 timer_id, u64 interval);
 
 void TW (tw_timer_stop) (TWT (tw_timer_wheel) * tw, u32 handle);
 
@@ -191,7 +223,9 @@ void TW (tw_timer_wheel_init) (TWT (tw_timer_wheel) * tw,
 
 void TW (tw_timer_wheel_free) (TWT (tw_timer_wheel) * tw);
 
-u32 TW (tw_timer_expire_timers) (TWT (tw_timer_wheel) * tw, f64 now);
+u32 *TW (tw_timer_expire_timers) (TWT (tw_timer_wheel) * tw, f64 now);
+u32 *TW (tw_timer_expire_timers_vec) (TWT (tw_timer_wheel) * tw, f64 now,
+				      u32 * vec);
 
 /*
  * fd.io coding-style-patch-verification: ON