perfmon plugin: 2-way parallel stat collection

As a FUD reduction measure, this patch implements 2-way parallel
counter collection. Synthetic stat component counter pairs run at the
same time. Running two counters (of any kind) at the same time
naturally reduces the aggregate time required by an approximate
factor-of-2, depending on whether an even or odd number of stats have
been requested.

I don't completely buy the argument that computing synthetic stats
such as instructions-per-clock will be inaccurate if component counter
values are collected sequentially. Given uniform traffic pattern, it
must make no difference.

As the collection interval increases, the difference between serial
and parallel component counter collection will approach zero, see also
the Central Limit theorem.

Change-Id: I36ebdcf125e8882cca8a1929ec58f17fba1ad8f1
Signed-off-by: Dave Barach <dave@barachs.net>

4 files changed, 54 insertions, 58 deletions

diff --git a/src/vlib/main.c b/src/vlib/main.c
index 23c4e076e1f..0e480fabe2a 100644
--- a/src/vlib/main.c
+++ b/src/vlib/main.c
@@ -543,15 +543,17 @@ never_inline void
 vlib_node_runtime_sync_stats (vlib_main_t * vm,
 			      vlib_node_runtime_t * r,
 			      uword n_calls, uword n_vectors, uword n_clocks,
-			      uword n_ticks)
+			      uword n_ticks0, uword n_ticks1)
 {
   vlib_node_t *n = vlib_get_node (vm, r->node_index);
 
   n->stats_total.calls += n_calls + r->calls_since_last_overflow;
   n->stats_total.vectors += n_vectors + r->vectors_since_last_overflow;
   n->stats_total.clocks += n_clocks + r->clocks_since_last_overflow;
-  n->stats_total.perf_counter_ticks += n_ticks +
-    r->perf_counter_ticks_since_last_overflow;
+  n->stats_total.perf_counter0_ticks += n_ticks0 +
+    r->perf_counter0_ticks_since_last_overflow;
+  n->stats_total.perf_counter1_ticks += n_ticks1 +
+    r->perf_counter1_ticks_since_last_overflow;
   n->stats_total.perf_counter_vectors += n_vectors +
     r->perf_counter_vectors_since_last_overflow;
   n->stats_total.max_clock = r->max_clock;
@@ -560,7 +562,8 @@ vlib_node_runtime_sync_stats (vlib_main_t * vm,
   r->calls_since_last_overflow = 0;
   r->vectors_since_last_overflow = 0;
   r->clocks_since_last_overflow = 0;
-  r->perf_counter_ticks_since_last_overflow = 0ULL;
+  r->perf_counter0_ticks_since_last_overflow = 0ULL;
+  r->perf_counter1_ticks_since_last_overflow = 0ULL;
   r->perf_counter_vectors_since_last_overflow = 0ULL;
 }
 
@@ -568,12 +571,12 @@ always_inline void __attribute__ ((unused))
 vlib_process_sync_stats (vlib_main_t * vm,
 			 vlib_process_t * p,
 			 uword n_calls, uword n_vectors, uword n_clocks,
-			 uword n_ticks)
+			 uword n_ticks0, uword n_ticks1)
 {
   vlib_node_runtime_t *rt = &p->node_runtime;
   vlib_node_t *n = vlib_get_node (vm, rt->node_index);
   vlib_node_runtime_sync_stats (vm, rt, n_calls, n_vectors, n_clocks,
-				n_ticks);
+				n_ticks0, n_ticks1);
   n->stats_total.suspends += p->n_suspends;
   p->n_suspends = 0;
 }
@@ -599,7 +602,7 @@ vlib_node_sync_stats (vlib_main_t * vm, vlib_node_t * n)
       vec_elt_at_index (vm->node_main.nodes_by_type[n->type],
 			n->runtime_index);
 
-  vlib_node_runtime_sync_stats (vm, rt, 0, 0, 0, 0);
+  vlib_node_runtime_sync_stats (vm, rt, 0, 0, 0, 0, 0);
 
   /* Sync up runtime next frame vector counters with main node structure. */
   {
@@ -620,27 +623,30 @@ vlib_node_runtime_update_stats (vlib_main_t * vm,
 				vlib_node_runtime_t * node,
 				uword n_calls,
 				uword n_vectors, uword n_clocks,
-				uword n_ticks)
+				uword n_ticks0, uword n_ticks1)
 {
   u32 ca0, ca1, v0, v1, cl0, cl1, r;
-  u32 ptick0, ptick1, pvec0, pvec1;
+  u32 ptick00, ptick01, ptick10, ptick11, pvec0, pvec1;
 
   cl0 = cl1 = node->clocks_since_last_overflow;
   ca0 = ca1 = node->calls_since_last_overflow;
   v0 = v1 = node->vectors_since_last_overflow;
-  ptick0 = ptick1 = node->perf_counter_ticks_since_last_overflow;
+  ptick00 = ptick01 = node->perf_counter0_ticks_since_last_overflow;
+  ptick10 = ptick11 = node->perf_counter1_ticks_since_last_overflow;
   pvec0 = pvec1 = node->perf_counter_vectors_since_last_overflow;
 
   ca1 = ca0 + n_calls;
   v1 = v0 + n_vectors;
   cl1 = cl0 + n_clocks;
-  ptick1 = ptick0 + n_ticks;
+  ptick01 = ptick00 + n_ticks0;
+  ptick11 = ptick10 + n_ticks1;
   pvec1 = pvec0 + n_vectors;
 
   node->calls_since_last_overflow = ca1;
   node->clocks_since_last_overflow = cl1;
   node->vectors_since_last_overflow = v1;
-  node->perf_counter_ticks_since_last_overflow = ptick1;
+  node->perf_counter0_ticks_since_last_overflow = ptick01;
+  node->perf_counter1_ticks_since_last_overflow = ptick11;
   node->perf_counter_vectors_since_last_overflow = pvec1;
 
   node->max_clock_n = node->max_clock > n_clocks ?
@@ -649,38 +655,39 @@ vlib_node_runtime_update_stats (vlib_main_t * vm,
 
   r = vlib_node_runtime_update_main_loop_vector_stats (vm, node, n_vectors);
 
-  if (PREDICT_FALSE (ca1 < ca0 || v1 < v0 || cl1 < cl0) || (ptick1 < ptick0)
-      || (pvec1 < pvec0))
+  if (PREDICT_FALSE (ca1 < ca0 || v1 < v0 || cl1 < cl0) || (ptick01 < ptick00)
+      || (ptick11 < ptick10) || (pvec1 < pvec0))
     {
       node->calls_since_last_overflow = ca0;
       node->clocks_since_last_overflow = cl0;
       node->vectors_since_last_overflow = v0;
-      node->perf_counter_ticks_since_last_overflow = ptick0;
+      node->perf_counter0_ticks_since_last_overflow = ptick00;
+      node->perf_counter1_ticks_since_last_overflow = ptick10;
       node->perf_counter_vectors_since_last_overflow = pvec0;
 
       vlib_node_runtime_sync_stats (vm, node, n_calls, n_vectors, n_clocks,
-				    n_ticks);
+				    n_ticks0, n_ticks1);
     }
 
   return r;
 }
 
-static inline u64
-vlib_node_runtime_perf_counter (vlib_main_t * vm)
+static inline void
+vlib_node_runtime_perf_counter (vlib_main_t * vm, u64 * pmc0, u64 * pmc1)
 {
+  *pmc0 = 0;
+  *pmc1 = 0;
   if (PREDICT_FALSE (vm->vlib_node_runtime_perf_counter_cb != 0))
-    return ((*vm->vlib_node_runtime_perf_counter_cb) (vm));
-  return 0ULL;
+    (*vm->vlib_node_runtime_perf_counter_cb) (vm, pmc0, pmc1);
 }
 
 always_inline void
 vlib_process_update_stats (vlib_main_t * vm,
 			   vlib_process_t * p,
-			   uword n_calls, uword n_vectors, uword n_clocks,
-			   uword n_ticks)
+			   uword n_calls, uword n_vectors, uword n_clocks)
 {
   vlib_node_runtime_update_stats (vm, &p->node_runtime,
-				  n_calls, n_vectors, n_clocks, n_ticks);
+				  n_calls, n_vectors, n_clocks, 0ULL, 0ULL);
 }
 
 static clib_error_t *
@@ -1098,6 +1105,8 @@ dispatch_pcap_trace (vlib_main_t * vm,
     }
 }
 
+u64 oingo0, oingo1;
+
 static_always_inline u64
 dispatch_node (vlib_main_t * vm,
 	       vlib_node_runtime_t * node,
@@ -1146,18 +1155,14 @@ dispatch_node (vlib_main_t * vm,
 
   if (1 /* || vm->thread_index == node->thread_index */ )
     {
-      u64 pmc_before, pmc_delta;
+      u64 pmc_before[2], pmc_after[2], pmc_delta[2];
 
       vlib_elog_main_loop_event (vm, node->node_index,
 				 last_time_stamp,
 				 frame ? frame->n_vectors : 0,
 				 /* is_after */ 0);
 
-      /*
-       * To validate accounting: pmc_before = last_time_stamp
-       * perf ticks should equal clocks/pkt...
-       */
-      pmc_before = vlib_node_runtime_perf_counter (vm);
+      vlib_node_runtime_perf_counter (vm, &pmc_before[0], &pmc_before[1]);
 
       /*
        * Turn this on if you run into
@@ -1191,7 +1196,10 @@ dispatch_node (vlib_main_t * vm,
        * To validate accounting: pmc_delta = t - pmc_before;
        * perf ticks should equal clocks/pkt...
        */
-      pmc_delta = vlib_node_runtime_perf_counter (vm) - pmc_before;
+      vlib_node_runtime_perf_counter (vm, &pmc_after[0], &pmc_after[1]);
+
+      pmc_delta[0] = pmc_after[0] - pmc_before[0];
+      pmc_delta[1] = pmc_after[1] - pmc_before[1];
 
       vlib_elog_main_loop_event (vm, node->node_index, t, n,	/* is_after */
 				 1);
@@ -1199,11 +1207,18 @@ dispatch_node (vlib_main_t * vm,
       vm->main_loop_vectors_processed += n;
       vm->main_loop_nodes_processed += n > 0;
 
+      if (pmc_delta[0] || pmc_delta[1])
+	{
+	  oingo0 += pmc_delta[0];
+	  oingo1 += pmc_delta[1];
+	}
+
       v = vlib_node_runtime_update_stats (vm, node,
 					  /* n_calls */ 1,
 					  /* n_vectors */ n,
 					  /* n_clocks */ t - last_time_stamp,
-					  pmc_delta /* PMC ticks */ );
+					  pmc_delta[0] /* PMC0 */ ,
+					  pmc_delta[1] /* PMC1 */ );
 
       /* When in interrupt mode and vector rate crosses threshold switch to
          polling mode. */
@@ -1542,8 +1557,7 @@ dispatch_process (vlib_main_t * vm,
   vlib_process_update_stats (vm, p,
 			     /* n_calls */ !is_suspend,
 			     /* n_vectors */ n_vectors,
-			     /* n_clocks */ t - last_time_stamp,
-			     /* pmc_ticks */ 0ULL);
+			     /* n_clocks */ t - last_time_stamp);
 
   return t;
 }
@@ -1626,8 +1640,7 @@ dispatch_suspended_process (vlib_main_t * vm,
   vlib_process_update_stats (vm, p,
 			     /* n_calls */ !is_suspend,
 			     /* n_vectors */ n_vectors,
-			     /* n_clocks */ t - last_time_stamp,
-			     /* pmc_ticks */ 0ULL);
+			     /* n_clocks */ t - last_time_stamp);
 
   return t;
 }
@@ -1677,9 +1690,6 @@ vlib_main_or_worker_loop (vlib_main_t * vm, int is_main)
   if (!nm->interrupt_threshold_vector_length)
     nm->interrupt_threshold_vector_length = 5;
 
-  /* Make sure the performance monitor counter is disabled */
-  vm->perf_counter_id = ~0;
-
   /* Start all processes. */
   if (is_main)
     {
diff --git a/src/vlib/main.h b/src/vlib/main.h
index 91661fdaaad..4c6d0f490dd 100644
--- a/src/vlib/main.h
+++ b/src/vlib/main.h
@@ -84,9 +84,8 @@ typedef struct vlib_main_t
   u32 node_counts_per_main_loop[2];
 
   /* Main loop hw / sw performance counters */
-    u64 (*vlib_node_runtime_perf_counter_cb) (struct vlib_main_t *);
-  int perf_counter_id;
-  int perf_counter_fd;
+  void (*vlib_node_runtime_perf_counter_cb) (struct vlib_main_t *,
+					     u64 *, u64 *);
 
   /* Every so often we switch to the next counter. */
 #define VLIB_LOG2_MAIN_LOOPS_PER_STATS_UPDATE 7
diff --git a/src/vlib/node.h b/src/vlib/node.h
index f41eb60aa2c..8bb89f44bc7 100644
--- a/src/vlib/node.h
+++ b/src/vlib/node.h
@@ -258,7 +258,8 @@ typedef struct
   u64 calls, vectors, clocks, suspends;
   u64 max_clock;
   u64 max_clock_n;
-  u64 perf_counter_ticks;
+  u64 perf_counter0_ticks;
+  u64 perf_counter1_ticks;
   u64 perf_counter_vectors;
 } vlib_node_stats_t;
 
@@ -507,7 +508,8 @@ typedef struct vlib_node_runtime_t
   u32 vectors_since_last_overflow;	/**< Number of vector elements
 					  processed by this node. */
 
-  u32 perf_counter_ticks_since_last_overflow; /**< Perf counter ticks */
+  u32 perf_counter0_ticks_since_last_overflow; /**< Perf counter 0 ticks */
+  u32 perf_counter1_ticks_since_last_overflow; /**< Perf counter 1 ticks */
   u32 perf_counter_vectors_since_last_overflow;	/**< Perf counter vectors */
 
   u32 next_frame_index;			/**< Start of next frames for this
diff --git a/src/vlib/node_cli.c b/src/vlib/node_cli.c
index 062854af5bc..ad17c1d6f4d 100644
--- a/src/vlib/node_cli.c
+++ b/src/vlib/node_cli.c
@@ -148,8 +148,6 @@ format_vlib_node_stats (u8 * s, va_list * va)
   f64 maxc, maxcn;
   u32 maxn;
   u32 indent;
-  u64 pmc_ticks;
-  f64 pmc_ticks_per_packet;
 
   if (!n)
     {
@@ -163,9 +161,6 @@ format_vlib_node_stats (u8 * s, va_list * va)
 		    "%=30s%=12s%=16s%=16s%=16s%=16s%=16s",
 		    "Name", "State", "Calls", "Vectors", "Suspends",
 		    "Clocks", "Vectors/Call");
-      if (vm->perf_counter_id)
-	s = format (s, "%=16s", "Perf Ticks");
-
       return s;
     }
 
@@ -182,13 +177,6 @@ format_vlib_node_stats (u8 * s, va_list * va)
   else
     maxcn = 0.0;
 
-  pmc_ticks = n->stats_total.perf_counter_ticks -
-    n->stats_last_clear.perf_counter_ticks;
-  if (p > 0)
-    pmc_ticks_per_packet = (f64) pmc_ticks / (f64) p;
-  else
-    pmc_ticks_per_packet = 0.0;
-
   /* Clocks per packet, per call or per suspend. */
   x = 0;
   if (p > 0)
@@ -221,9 +209,6 @@ format_vlib_node_stats (u8 * s, va_list * va)
     s = format (s, "%-30v%=12U%16Ld%16Ld%16Ld%16.2e%16.2f", ns,
 		format_vlib_node_state, vm, n, c, p, d, x, v);
 
-  if (pmc_ticks_per_packet > 0.0)
-    s = format (s, "%16.2e", pmc_ticks_per_packet);
-
   if (ns != n->name)
     vec_free (ns);