switch vlib process model to tw_timer_template timer impl

Change-Id: I36bb47faea55a6fea7af7ee58d87d8f6dd28f93d
Signed-off-by: Dave Barach <dave@barachs.net>

13 files changed, 197 insertions, 77 deletions

diff --git a/src/vlib/main.c b/src/vlib/main.c
index 14f680e61fc..19d70232e6e 100644
--- a/src/vlib/main.c
+++ b/src/vlib/main.c
@@ -41,6 +41,7 @@
 #include <vppinfra/format.h>
 #include <vlib/vlib.h>
 #include <vlib/threads.h>
+#include <vppinfra/tw_timer_1t_3w_1024sl_ov.h>
 
 #include <vlib/unix/cj.h>
 
@@ -1341,9 +1342,16 @@ dispatch_process (vlib_main_t * vm,
       p->suspended_process_frame_index = pf - nm->suspended_process_frames;
 
       if (p->flags & VLIB_PROCESS_IS_SUSPENDED_WAITING_FOR_CLOCK)
-	timing_wheel_insert (&nm->timing_wheel, p->resume_cpu_time,
-			     vlib_timing_wheel_data_set_suspended_process
-			     (node->runtime_index));
+	{
+	  TWT (tw_timer_wheel) * tw =
+	    (TWT (tw_timer_wheel) *) nm->timing_wheel;
+	  p->stop_timer_handle =
+	    TW (tw_timer_start) (tw,
+				 vlib_timing_wheel_data_set_suspended_process
+				 (node->runtime_index) /* [sic] pool idex */ ,
+				 0 /* timer_id */ ,
+				 p->resume_clock_interval);
+	}
     }
   else
     p->flags &= ~VLIB_PROCESS_IS_RUNNING;
@@ -1416,9 +1424,14 @@ dispatch_suspended_process (vlib_main_t * vm,
       n_vectors = 0;
       p->n_suspends += 1;
       if (p->flags & VLIB_PROCESS_IS_SUSPENDED_WAITING_FOR_CLOCK)
-	timing_wheel_insert (&nm->timing_wheel, p->resume_cpu_time,
-			     vlib_timing_wheel_data_set_suspended_process
-			     (node->runtime_index));
+	{
+	  p->stop_timer_handle =
+	    TW (tw_timer_start) ((TWT (tw_timer_wheel) *) nm->timing_wheel,
+				 vlib_timing_wheel_data_set_suspended_process
+				 (node->runtime_index) /* [sic] pool idex */ ,
+				 0 /* timer_id */ ,
+				 p->resume_clock_interval);
+	}
     }
   else
     {
@@ -1465,17 +1478,6 @@ vlib_main_or_worker_loop (vlib_main_t * vm, int is_main)
   else
     cpu_time_now = clib_cpu_time_now ();
 
-  /* Arrange for first level of timing wheel to cover times we care
-     most about. */
-  if (is_main)
-    {
-      nm->timing_wheel.min_sched_time = 10e-6;
-      nm->timing_wheel.max_sched_time = 10e-3;
-      timing_wheel_init (&nm->timing_wheel,
-			 cpu_time_now, vm->clib_time.clocks_per_second);
-      vec_alloc (nm->data_from_advancing_timing_wheel, 32);
-    }
-
   /* Pre-allocate interupt runtime indices and lock. */
   vec_alloc (nm->pending_interrupt_node_runtime_indices, 32);
   vec_alloc (last_node_runtime_indices, 32);
@@ -1561,12 +1563,15 @@ vlib_main_or_worker_loop (vlib_main_t * vm, int is_main)
       if (is_main)
 	{
 	  /* Check if process nodes have expired from timing wheel. */
-	  nm->data_from_advancing_timing_wheel
-	    = timing_wheel_advance (&nm->timing_wheel, cpu_time_now,
-				    nm->data_from_advancing_timing_wheel,
-				    &nm->cpu_time_next_process_ready);
+	  ASSERT (nm->data_from_advancing_timing_wheel != 0);
+
+	  nm->data_from_advancing_timing_wheel =
+	    TW (tw_timer_expire_timers_vec)
+	    ((TWT (tw_timer_wheel) *) nm->timing_wheel, vlib_time_now (vm),
+	     nm->data_from_advancing_timing_wheel);
 
 	  ASSERT (nm->data_from_advancing_timing_wheel != 0);
+
 	  if (PREDICT_FALSE
 	      (_vec_len (nm->data_from_advancing_timing_wheel) > 0))
 	    {
@@ -1612,8 +1617,6 @@ vlib_main_or_worker_loop (vlib_main_t * vm, int is_main)
 			dispatch_suspended_process (vm, di, cpu_time_now);
 		    }
 		}
-
-	      /* Reset vector. */
 	      _vec_len (nm->data_from_advancing_timing_wheel) = 0;
 	    }
 	}
@@ -1692,6 +1695,7 @@ int
 vlib_main (vlib_main_t * volatile vm, unformat_input_t * input)
 {
   clib_error_t *volatile error;
+  vlib_node_main_t *nm = &vm->node_main;
 
   vm->queue_signal_callback = dummy_queue_signal_callback;
 
@@ -1746,6 +1750,18 @@ vlib_main (vlib_main_t * volatile vm, unformat_input_t * input)
 				       VLIB_BUFFER_DEFAULT_FREE_LIST_BYTES,
 				       "default");
 
+  nm->timing_wheel = clib_mem_alloc_aligned (sizeof (TWT (tw_timer_wheel)),
+					     CLIB_CACHE_LINE_BYTES);
+
+  vec_validate (nm->data_from_advancing_timing_wheel, 10);
+  _vec_len (nm->data_from_advancing_timing_wheel) = 0;
+
+  /* Create the process timing wheel */
+  TW (tw_timer_wheel_init) ((TWT (tw_timer_wheel) *) nm->timing_wheel,
+			    0 /* no callback */ ,
+			    10e-6 /* timer period 10us */ ,
+			    ~0 /* max expirations per call */ );
+
   switch (clib_setjmp (&vm->main_loop_exit, VLIB_MAIN_LOOP_EXIT_NONE))
     {
     case VLIB_MAIN_LOOP_EXIT_NONE:
diff --git a/src/vlib/node.h b/src/vlib/node.h
index 906d795fe23..77914272bbc 100644
--- a/src/vlib/node.h
+++ b/src/vlib/node.h
@@ -43,7 +43,6 @@
 #include <vppinfra/cpu.h>
 #include <vppinfra/longjmp.h>
 #include <vppinfra/lock.h>
-#include <vppinfra/timing_wheel.h>
 #include <vlib/trace.h>		/* for vlib_trace_filter_t */
 
 /* Forward declaration. */
@@ -542,8 +541,14 @@ typedef struct
   /* Pool of currently valid event types. */
   vlib_process_event_type_t *event_type_pool;
 
-  /* When suspending saves cpu cycle counter when process is to be resumed. */
-  u64 resume_cpu_time;
+  /*
+   * When suspending saves clock time (10us ticks) when process
+   * is to be resumed.
+   */
+  u64 resume_clock_interval;
+
+  /* Handle from timer code, to cancel an unexpired timer */
+  u32 stop_timer_handle;
 
   /* Default output function and its argument for any CLI outputs
      within the process. */
@@ -664,7 +669,7 @@ typedef struct
   vlib_pending_frame_t *pending_frames;
 
   /* Timing wheel for scheduling time-based node dispatch. */
-  timing_wheel_t timing_wheel;
+  void *timing_wheel;
 
   vlib_signal_timed_event_data_t *signal_timed_event_data_pool;
 
@@ -672,7 +677,7 @@ typedef struct
   u32 *data_from_advancing_timing_wheel;
 
   /* CPU time of next process to be ready on timing wheel. */
-  u64 cpu_time_next_process_ready;
+  f64 time_next_process_ready;
 
   /* Vector of process nodes.
      One for each node of type VLIB_NODE_TYPE_PROCESS. */
diff --git a/src/vlib/node_funcs.h b/src/vlib/node_funcs.h
index 4d7cc1928f3..d6588a74ba1 100644
--- a/src/vlib/node_funcs.h
+++ b/src/vlib/node_funcs.h
@@ -46,6 +46,7 @@
 #define included_vlib_node_funcs_h
 
 #include <vppinfra/fifo.h>
+#include <vppinfra/tw_timer_1t_3w_1024sl_ov.h>
 
 /** \brief Get vlib node by index.
  @warning This function will ASSERT if @c i is out of range.
@@ -428,14 +429,14 @@ vlib_current_process (vlib_main_t * vm)
   return vlib_get_current_process (vm)->node_runtime.node_index;
 }
 
-/** Returns TRUE if a process suspend time is less than 1us
+/** Returns TRUE if a process suspend time is less than 10us
     @param dt - remaining poll time in seconds
-    @returns 1 if dt < 1e-6, 0 otherwise
+    @returns 1 if dt < 10e-6, 0 otherwise
 */
 always_inline uword
 vlib_process_suspend_time_is_zero (f64 dt)
 {
-  return dt < 1e-6;
+  return dt < 10e-6;
 }
 
 /** Suspend a vlib cooperative multi-tasking thread for a period of time
@@ -450,7 +451,6 @@ vlib_process_suspend (vlib_main_t * vm, f64 dt)
   uword r;
   vlib_node_main_t *nm = &vm->node_main;
   vlib_process_t *p = vec_elt (nm->processes, nm->current_process_index);
-  u64 dt_cpu = dt * vm->clib_time.clocks_per_second;
 
   if (vlib_process_suspend_time_is_zero (dt))
     return VLIB_PROCESS_RESUME_LONGJMP_RESUME;
@@ -459,7 +459,8 @@ vlib_process_suspend (vlib_main_t * vm, f64 dt)
   r = clib_setjmp (&p->resume_longjmp, VLIB_PROCESS_RESUME_LONGJMP_SUSPEND);
   if (r == VLIB_PROCESS_RESUME_LONGJMP_SUSPEND)
     {
-      p->resume_cpu_time = clib_cpu_time_now () + dt_cpu;
+      /* expiration time in 10us ticks */
+      p->resume_clock_interval = dt * 1e5;
       clib_longjmp (&p->return_longjmp, VLIB_PROCESS_RETURN_LONGJMP_SUSPEND);
     }
 
@@ -718,8 +719,7 @@ vlib_process_wait_for_event_or_clock (vlib_main_t * vm, f64 dt)
   r = clib_setjmp (&p->resume_longjmp, VLIB_PROCESS_RESUME_LONGJMP_SUSPEND);
   if (r == VLIB_PROCESS_RESUME_LONGJMP_SUSPEND)
     {
-      p->resume_cpu_time = (clib_cpu_time_now ()
-			    + (dt * vm->clib_time.clocks_per_second));
+      p->resume_clock_interval = dt * 1e5;
       clib_longjmp (&p->return_longjmp, VLIB_PROCESS_RETURN_LONGJMP_SUSPEND);
     }
 
@@ -834,7 +834,8 @@ vlib_process_signal_event_helper (vlib_node_main_t * nm,
       p->flags = p_flags | VLIB_PROCESS_RESUME_PENDING;
       vec_add1 (nm->data_from_advancing_timing_wheel, x);
       if (delete_from_wheel)
-	timing_wheel_delete (&nm->timing_wheel, x);
+	TW (tw_timer_stop) ((TWT (tw_timer_wheel) *) nm->timing_wheel,
+			    p->stop_timer_handle);
     }
 
   return data_to_be_written_by_caller;
@@ -895,7 +896,6 @@ vlib_process_signal_event_at_time (vlib_main_t * vm,
   else
     {
       vlib_signal_timed_event_data_t *te;
-      u64 dt_cpu = dt * vm->clib_time.clocks_per_second;
 
       pool_get_aligned (nm->signal_timed_event_data_pool, te, sizeof (te[0]));
 
@@ -911,10 +911,12 @@ vlib_process_signal_event_at_time (vlib_main_t * vm,
       te->process_node_index = n->runtime_index;
       te->event_type_index = t;
 
-      timing_wheel_insert (&nm->timing_wheel, clib_cpu_time_now () + dt_cpu,
-			   vlib_timing_wheel_data_set_timed_event (te -
-								   nm->
-								   signal_timed_event_data_pool));
+      p->stop_timer_handle =
+	TW (tw_timer_start) ((TWT (tw_timer_wheel) *) nm->timing_wheel,
+			     vlib_timing_wheel_data_set_timed_event
+			     (te - nm->signal_timed_event_data_pool),
+			     0 /* timer_id */ ,
+			     (vlib_time_now (vm) + dt) * 1e5);
 
       /* Inline data big enough to hold event? */
       if (te->n_data_bytes < sizeof (te->inline_event_data))
diff --git a/src/vlib/unix/input.c b/src/vlib/unix/input.c
index 73783d13c89..515dae94811 100644
--- a/src/vlib/unix/input.c
+++ b/src/vlib/unix/input.c
@@ -40,6 +40,7 @@
 #include <vlib/vlib.h>
 #include <vlib/unix/unix.h>
 #include <signal.h>
+#include <vppinfra/tw_timer_1t_3w_1024sl_ov.h>
 
 /* FIXME autoconf */
 #define HAVE_LINUX_EPOLL
@@ -113,56 +114,44 @@ linux_epoll_input (vlib_main_t * vm,
 
   {
     vlib_node_main_t *nm = &vm->node_main;
-    u64 t = nm->cpu_time_next_process_ready;
+    u32 ticks_until_expiration;
     f64 timeout;
-    int timeout_ms, max_timeout_ms = 10;
+    int timeout_ms = 0, max_timeout_ms = 10;
     f64 vector_rate = vlib_last_vectors_per_main_loop (vm);
 
-    if (t == ~0ULL)
+    /* If we're not working very hard, decide how long to sleep */
+    if (vector_rate < 2 && vm->api_queue_nonempty == 0
+	&& nm->input_node_counts_by_state[VLIB_NODE_STATE_POLLING] == 0)
       {
-	timeout = 10e-3;
-	timeout_ms = max_timeout_ms;
-      }
-    else
-      {
-	timeout =
-	  (((i64) t - (i64) clib_cpu_time_now ())
-	   * vm->clib_time.seconds_per_clock)
-	  /* subtract off some slop time */  - 50e-6;
+	ticks_until_expiration = TW (tw_timer_first_expires_in_ticks)
+	  ((TWT (tw_timer_wheel) *) nm->timing_wheel);
 
-	if (timeout < 1e-3)
+	/* Nothing on the fast wheel, sleep 10ms */
+	if (ticks_until_expiration == TW_SLOTS_PER_RING)
 	  {
-	    /* We have event happenning in less than 1 ms so
-	       don't allow epoll to wait */
-	    timeout_ms = 0;
+	    timeout = 10e-3;
+	    timeout_ms = max_timeout_ms;
 	  }
 	else
 	  {
-	    timeout_ms = timeout * 1e3;
-
-	    /* Must be between 1 and 10 ms. */
-	    timeout_ms = clib_max (1, timeout_ms);
-	    timeout_ms = clib_min (max_timeout_ms, timeout_ms);
+	    timeout = (f64) ticks_until_expiration *1e-5;
+	    if (timeout < 1e-3)
+	      timeout_ms = 0;
+	    else
+	      {
+		timeout_ms = timeout * 1e3;
+		/* Must be between 1 and 10 ms. */
+		timeout_ms = clib_max (1, timeout_ms);
+		timeout_ms = clib_min (max_timeout_ms, timeout_ms);
+	      }
 	  }
+	node->input_main_loops_per_call = 0;
       }
-
-    /* If we still have input nodes polling (e.g. vnet packet generator)
-       don't sleep. */
-    if (nm->input_node_counts_by_state[VLIB_NODE_STATE_POLLING] > 0)
-      timeout_ms = 0;
-
-    /*
-     * When busy: don't wait & only epoll for input
-     * every 1024 times through main loop.
-     */
-    if (vector_rate > 1 || vm->api_queue_nonempty)
+    else			/* busy */
       {
-	timeout_ms = 0;
+	/* Don't come back for a respectable number of dispatch cycles */
 	node->input_main_loops_per_call = 1024;
       }
-    else
-      /* We're not busy; go to sleep for a while. */
-      node->input_main_loops_per_call = 0;
 
     /* Allow any signal to wakeup our sleep. */
     {
diff --git a/src/vnet/lisp-cp/control.h b/src/vnet/lisp-cp/control.h
index 577035c4f42..0e63b3c7454 100644
--- a/src/vnet/lisp-cp/control.h
+++ b/src/vnet/lisp-cp/control.h
@@ -19,6 +19,7 @@
 #include <vnet/vnet.h>
 #include <vnet/lisp-cp/gid_dictionary.h>
 #include <vnet/lisp-cp/lisp_types.h>
+#include <vppinfra/timing_wheel.h>
 
 #define NUMBER_OF_RETRIES                   1
 #define PENDING_MREQ_EXPIRATION_TIME        3.0	/* seconds */
diff --git a/src/vppinfra/tw_timer_16t_1w_2048sl.h b/src/vppinfra/tw_timer_16t_1w_2048sl.h
index 6edef17bf60..66cf7d37b68 100644
--- a/src/vppinfra/tw_timer_16t_1w_2048sl.h
+++ b/src/vppinfra/tw_timer_16t_1w_2048sl.h
@@ -25,6 +25,8 @@
 #undef LOG2_TW_TIMERS_PER_OBJECT
 #undef TW_SUFFIX
 #undef TW_OVERFLOW_VECTOR
+#undef TW_FAST_WHEEL_BITMAP
+#undef TW_TIMER_ALLOW_DUPLICATE_STOP
 
 #define TW_TIMER_WHEELS 1
 #define TW_SLOTS_PER_RING 2048
@@ -33,6 +35,8 @@
 #define TW_TIMERS_PER_OBJECT 16
 #define LOG2_TW_TIMERS_PER_OBJECT 4
 #define TW_SUFFIX _16t_1w_2048sl
+#define TW_FAST_WHEEL_BITMAP 0
+#define TW_TIMER_ALLOW_DUPLICATE_STOP 0
 
 #include <vppinfra/tw_timer_template.h>
 
diff --git a/src/vppinfra/tw_timer_16t_2w_512sl.h b/src/vppinfra/tw_timer_16t_2w_512sl.h
index 2497b31c1ad..00587b8eeda 100644
--- a/src/vppinfra/tw_timer_16t_2w_512sl.h
+++ b/src/vppinfra/tw_timer_16t_2w_512sl.h
@@ -25,6 +25,8 @@
 #undef LOG2_TW_TIMERS_PER_OBJECT
 #undef TW_SUFFIX
 #undef TW_OVERFLOW_VECTOR
+#undef TW_FAST_WHEEL_BITMAP
+#undef TW_TIMER_ALLOW_DUPLICATE_STOP
 
 #define TW_TIMER_WHEELS 2
 #define TW_SLOTS_PER_RING 512
@@ -33,6 +35,8 @@
 #define TW_TIMERS_PER_OBJECT 16
 #define LOG2_TW_TIMERS_PER_OBJECT 4
 #define TW_SUFFIX _16t_2w_512sl
+#define TW_FAST_WHEEL_BITMAP 0
+#define TW_TIMER_ALLOW_DUPLICATE_STOP 0
 
 #include <vppinfra/tw_timer_template.h>
 
diff --git a/src/vppinfra/tw_timer_1t_3w_1024sl_ov.h b/src/vppinfra/tw_timer_1t_3w_1024sl_ov.h
index 7327f87b900..e5e4cc19a90 100644
--- a/src/vppinfra/tw_timer_1t_3w_1024sl_ov.h
+++ b/src/vppinfra/tw_timer_1t_3w_1024sl_ov.h
@@ -25,6 +25,8 @@
 #undef LOG2_TW_TIMERS_PER_OBJECT
 #undef TW_SUFFIX
 #undef TW_OVERFLOW_VECTOR
+#undef TW_FAST_WHEEL_BITMAP
+#undef TW_TIMER_ALLOW_DUPLICATE_STOP
 
 #define TW_TIMER_WHEELS 3
 #define TW_SLOTS_PER_RING 1024
@@ -34,6 +36,8 @@
 #define LOG2_TW_TIMERS_PER_OBJECT 0
 #define TW_SUFFIX _1t_3w_1024sl_ov
 #define TW_OVERFLOW_VECTOR 1
+#define TW_FAST_WHEEL_BITMAP 1
+#define TW_TIMER_ALLOW_DUPLICATE_STOP 1
 
 #include <vppinfra/tw_timer_template.h>
 
diff --git a/src/vppinfra/tw_timer_2t_1w_2048sl.h b/src/vppinfra/tw_timer_2t_1w_2048sl.h
index 33b74405fcc..98b548b39d4 100644
--- a/src/vppinfra/tw_timer_2t_1w_2048sl.h
+++ b/src/vppinfra/tw_timer_2t_1w_2048sl.h
@@ -25,6 +25,8 @@
 #undef LOG2_TW_TIMERS_PER_OBJECT
 #undef TW_SUFFIX
 #undef TW_OVERFLOW_VECTOR
+#undef TW_FAST_WHEEL_BITMAP
+#undef TW_TIMER_ALLOW_DUPLICATE_STOP
 
 #define TW_TIMER_WHEELS 1
 #define TW_SLOTS_PER_RING 2048
@@ -33,6 +35,8 @@
 #define TW_TIMERS_PER_OBJECT 2
 #define LOG2_TW_TIMERS_PER_OBJECT 1
 #define TW_SUFFIX _2t_1w_2048sl
+#define TW_FAST_WHEEL_BITMAP 0
+#define TW_TIMER_ALLOW_DUPLICATE_STOP 0
 
 #include <vppinfra/tw_timer_template.h>
 
diff --git a/src/vppinfra/tw_timer_4t_3w_256sl.h b/src/vppinfra/tw_timer_4t_3w_256sl.h
index 89adb7a2464..07203de8742 100644
--- a/src/vppinfra/tw_timer_4t_3w_256sl.h
+++ b/src/vppinfra/tw_timer_4t_3w_256sl.h
@@ -25,6 +25,8 @@
 #undef LOG2_TW_TIMERS_PER_OBJECT
 #undef TW_SUFFIX
 #undef TW_OVERFLOW_VECTOR
+#undef TW_FAST_WHEEL_BITMAP
+#undef TW_TIMER_ALLOW_DUPLICATE_STOP
 
 #define TW_TIMER_WHEELS 3
 #define TW_SLOTS_PER_RING 256
@@ -33,6 +35,8 @@
 #define TW_TIMERS_PER_OBJECT 4
 #define LOG2_TW_TIMERS_PER_OBJECT 2
 #define TW_SUFFIX _4t_3w_256sl
+#define TW_FAST_WHEEL_BITMAP 0
+#define TW_TIMER_ALLOW_DUPLICATE_STOP 0
 
 #include <vppinfra/tw_timer_template.h>
 
diff --git a/src/vppinfra/tw_timer_4t_3w_4sl_ov.h b/src/vppinfra/tw_timer_4t_3w_4sl_ov.h
index 0f76164d069..20a01d05e7d 100644
--- a/src/vppinfra/tw_timer_4t_3w_4sl_ov.h
+++ b/src/vppinfra/tw_timer_4t_3w_4sl_ov.h
@@ -25,6 +25,8 @@
 #undef LOG2_TW_TIMERS_PER_OBJECT
 #undef TW_SUFFIX
 #undef TW_OVERFLOW_VECTOR
+#undef TW_FAST_WHEEL_BITMAP
+#undef TW_TIMER_ALLOW_DUPLICATE_STOP
 
 #define TW_TIMER_WHEELS 3
 #define TW_SLOTS_PER_RING 4
@@ -34,6 +36,8 @@
 #define LOG2_TW_TIMERS_PER_OBJECT 2
 #define TW_SUFFIX _4t_3w_4sl_ov
 #define TW_OVERFLOW_VECTOR 1
+#define TW_FAST_WHEEL_BITMAP 0
+#define TW_TIMER_ALLOW_DUPLICATE_STOP 0
 
 #include <vppinfra/tw_timer_template.h>
 
diff --git a/src/vppinfra/tw_timer_template.c b/src/vppinfra/tw_timer_template.c
index 9253488ceac..c0a9685aa82 100644
--- a/src/vppinfra/tw_timer_template.c
+++ b/src/vppinfra/tw_timer_template.c
@@ -204,6 +204,11 @@ TW (tw_timer_start) (TWT (tw_timer_wheel) * tw, u32 pool_index, u32 timer_id,
   ts = &tw->w[TW_TIMER_RING_FAST][fast_ring_offset];
 
   timer_addhead (tw->timers, ts->head_index, t - tw->timers);
+
+#if TW_FAST_WHEEL_BITMAP
+  tw->fast_slot_bitmap = clib_bitmap_set (tw->fast_slot_bitmap,
+					  fast_ring_offset, 1);
+#endif
   return t - tw->timers;
 }
 
@@ -251,6 +256,16 @@ void TW (tw_timer_stop) (TWT (tw_timer_wheel) * tw, u32 handle)
 {
   TWT (tw_timer) * t;
 
+#if TW_TIMER_ALLOW_DUPLICATE_STOP
+  /*
+   * A vlib process may have its timer expire, and receive
+   * an event before the expiration is processed.
+   * That results in a duplicate tw_timer_stop.
+   */
+  if (pool_is_free_index (tw->timers, handle))
+    return;
+#endif
+
   t = pool_elt_at_index (tw->timers, handle);
 
   /* in case of idiotic handle (e.g. passing a listhead index) */
@@ -481,6 +496,11 @@ static inline
 		{
 		  ts = &tw->w[TW_TIMER_RING_FAST][t->fast_ring_offset];
 		  timer_addhead (tw->timers, ts->head_index, t - tw->timers);
+#if TW_FAST_WHEEL_BITMAP
+		  tw->fast_slot_bitmap =
+		    clib_bitmap_set (tw->fast_slot_bitmap,
+				     t->fast_ring_offset, 1);
+#endif
 		}
 	    }
 	}
@@ -523,6 +543,11 @@ static inline
 		{
 		  ts = &tw->w[TW_TIMER_RING_FAST][t->fast_ring_offset];
 		  timer_addhead (tw->timers, ts->head_index, t - tw->timers);
+#if TW_FAST_WHEEL_BITMAP
+		  tw->fast_slot_bitmap =
+		    clib_bitmap_set (tw->fast_slot_bitmap,
+				     t->fast_ring_offset, 1);
+#endif
 		}
 	      else		/* typical case */
 		{
@@ -569,6 +594,11 @@ static inline
 		  /* 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);
+#if TW_FAST_WHEEL_BITMAP
+		  tw->fast_slot_bitmap =
+		    clib_bitmap_set (tw->fast_slot_bitmap,
+				     t->fast_ring_offset, 1);
+#endif
 		}
 	    }
 	}
@@ -604,6 +634,12 @@ static inline
 	    }
 	  tw->expired_timer_handles = callback_vector;
 	}
+
+#if TW_FAST_WHEEL_BITMAP
+      tw->fast_slot_bitmap = clib_bitmap_set (tw->fast_slot_bitmap,
+					      fast_wheel_index, 0);
+#endif
+
       tw->current_tick++;
       fast_wheel_index++;
       tw->current_index[TW_TIMER_RING_FAST] = fast_wheel_index;
@@ -642,6 +678,44 @@ u32 *TW (tw_timer_expire_timers_vec) (TWT (tw_timer_wheel) * tw, f64 now,
   return TW (tw_timer_expire_timers_internal) (tw, now, vec);
 }
 
+#if TW_FAST_WHEEL_BITMAP
+/** Returns an approximation to the first timer expiration in
+ * timer-ticks from "now". To avoid wasting an unjustifiable
+ * amount of time on the problem, we maintain an approximate fast-wheel slot
+ * occupancy bitmap. We don't worry about clearing fast wheel bits
+ * when timers are removed from fast wheel slots.
+ */
+
+u32 TW (tw_timer_first_expires_in_ticks) (TWT (tw_timer_wheel) * tw)
+{
+  u32 first_expiring_index, fast_ring_index;
+  i32 delta;
+
+  if (clib_bitmap_is_zero (tw->fast_slot_bitmap))
+    return TW_SLOTS_PER_RING;
+
+  fast_ring_index = tw->current_index[TW_TIMER_RING_FAST];
+  if (fast_ring_index == TW_SLOTS_PER_RING)
+    fast_ring_index = 0;
+
+  first_expiring_index = clib_bitmap_next_set (tw->fast_slot_bitmap,
+					       fast_ring_index);
+  if (first_expiring_index == ~0 && fast_ring_index != 0)
+    first_expiring_index = clib_bitmap_first_set (tw->fast_slot_bitmap);
+
+  ASSERT (first_expiring_index != ~0);
+
+  delta = (i32) first_expiring_index - (i32) fast_ring_index;
+  if (delta < 0)
+    delta += TW_SLOTS_PER_RING;
+
+  ASSERT (delta >= 0);
+
+  return (u32) delta;
+}
+
+#endif
+
 /*
  * fd.io coding-style-patch-verification: ON
  *
diff --git a/src/vppinfra/tw_timer_template.h b/src/vppinfra/tw_timer_template.h
index 76755609451..0404e3f4715 100644
--- a/src/vppinfra/tw_timer_template.h
+++ b/src/vppinfra/tw_timer_template.h
@@ -19,6 +19,7 @@
 
 #include <vppinfra/clib.h>
 #include <vppinfra/pool.h>
+#include <vppinfra/bitmap.h>
 
 #ifndef _twt
 #define _twt(a,b) a##b##_t
@@ -202,6 +203,11 @@ typedef struct
   tw_timer_wheel_slot_t overflow;
 #endif
 
+#if TW_FAST_WHEEL_BITMAP > 0
+  /** Fast wheel slot occupancy bitmap */
+  uword *fast_slot_bitmap;
+#endif
+
   /** expired timer callback, receives a vector of handles */
   void (*expired_timer_callback) (u32 * expired_timer_handles);
 
@@ -226,6 +232,9 @@ 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_vec) (TWT (tw_timer_wheel) * tw, f64 now,
 				      u32 * vec);
+#if TW_FAST_WHEEL_BITMAP
+u32 TW (tw_timer_first_expires_in_ticks) (TWT (tw_timer_wheel) * tw);
+#endif
 
 /*
  * fd.io coding-style-patch-verification: ON