Clean up multi-thread barrier-sync hold-down timer

Main thread: don't bother with the barrier sync hold-down timer if
none of the worker threads are busy.

Worker threads: avoid epoll_pwait (10ms timeout) when the
control-plane has been active in the last half-second.

Change-Id: I82008d09968c65e2a4af0ebb7887389992e60603
Signed-off-by: Dave Barach <dave@barachs.net>
(cherry picked from commit 9ae190e9d228bfc1358482d4f07da1f4cfd41c90)

2 files changed, 57 insertions, 13 deletions

diff --git a/src/vlib/threads.c b/src/vlib/threads.c
index 7d17c7b37cc..52886df37e0 100644
--- a/src/vlib/threads.c
+++ b/src/vlib/threads.c
@@ -1389,7 +1389,9 @@ vlib_worker_thread_barrier_sync_int (vlib_main_t * vm, const char *func_name)
   f64 t_entry;
   f64 t_open;
   f64 t_closed;
+  f64 max_vector_rate;
   u32 count;
+  int i;
 
   if (vec_len (vlib_mains) < 2)
     return;
@@ -1410,23 +1412,41 @@ vlib_worker_thread_barrier_sync_int (vlib_main_t * vm, const char *func_name)
       return;
     }
 
+  /*
+   * Need data to decide if we're working hard enough to honor
+   * the barrier hold-down timer.
+   */
+  max_vector_rate = 0.0;
+  for (i = 1; i < vec_len (vlib_mains); i++)
+    max_vector_rate =
+      clib_max (max_vector_rate,
+		vlib_last_vectors_per_main_loop_as_f64 (vlib_mains[i]));
+
   vlib_worker_threads[0].barrier_sync_count++;
 
   /* Enforce minimum barrier open time to minimize packet loss */
   ASSERT (vm->barrier_no_close_before <= (now + BARRIER_MINIMUM_OPEN_LIMIT));
 
-  while (1)
+  /*
+   * If any worker thread seems busy, which we define
+   * as a vector rate above 10, we enforce the barrier hold-down timer
+   */
+  if (max_vector_rate > 10.0)
     {
-      now = vlib_time_now (vm);
-      /* Barrier hold-down timer expired? */
-      if (now >= vm->barrier_no_close_before)
-	break;
-      if ((vm->barrier_no_close_before - now)
-	  > (2.0 * BARRIER_MINIMUM_OPEN_LIMIT))
+      while (1)
 	{
-	  clib_warning ("clock change: would have waited for %.4f seconds",
-			(vm->barrier_no_close_before - now));
-	  break;
+	  now = vlib_time_now (vm);
+	  /* Barrier hold-down timer expired? */
+	  if (now >= vm->barrier_no_close_before)
+	    break;
+	  if ((vm->barrier_no_close_before - now)
+	      > (2.0 * BARRIER_MINIMUM_OPEN_LIMIT))
+	    {
+	      clib_warning
+		("clock change: would have waited for %.4f seconds",
+		 (vm->barrier_no_close_before - now));
+	      break;
+	    }
 	}
     }
   /* Record time of closure */
diff --git a/src/vlib/unix/input.c b/src/vlib/unix/input.c
index 7f49b954cc2..1c1cb1aa79c 100644
--- a/src/vlib/unix/input.c
+++ b/src/vlib/unix/input.c
@@ -145,9 +145,13 @@ linux_epoll_input_inline (vlib_main_t * vm, vlib_node_runtime_t * node,
     vlib_node_main_t *nm = &vm->node_main;
     u32 ticks_until_expiration;
     f64 timeout;
+    f64 now;
     int timeout_ms = 0, max_timeout_ms = 10;
     f64 vector_rate = vlib_last_vectors_per_main_loop (vm);
 
+    if (is_main == 0)
+      now = vlib_time_now (vm);
+
     /*
      * If we've been asked for a fixed-sleep between main loop polls,
      * do so right away.
@@ -194,8 +198,9 @@ linux_epoll_input_inline (vlib_main_t * vm, vlib_node_runtime_t * node,
 	  }
 	node->input_main_loops_per_call = 0;
       }
-    else if (is_main == 0 && vector_rate < 2 &&
-	     nm->input_node_counts_by_state[VLIB_NODE_STATE_POLLING] == 0)
+    else if (is_main == 0 && vector_rate < 2
+	     && (vlib_global_main.time_last_barrier_release + 0.5 < now)
+	     && nm->input_node_counts_by_state[VLIB_NODE_STATE_POLLING] == 0)
       {
 	timeout = 10e-3;
 	timeout_ms = max_timeout_ms;
@@ -227,8 +232,27 @@ linux_epoll_input_inline (vlib_main_t * vm, vlib_node_runtime_t * node,
       }
     else
       {
+	/*
+	 * Worker thread, no epoll fd's, sleep for 100us at a time
+	 * and check for a barrier sync request
+	 */
 	if (timeout_ms)
-	  usleep (timeout_ms * 1000);
+	  {
+	    struct timespec ts, tsrem;
+	    f64 limit = now + (f64) timeout_ms * 1e-3;
+
+	    while (vlib_time_now (vm) < limit)
+	      {
+		/* Sleep for 100us at a time */
+		ts.tv_sec = 0;
+		ts.tv_nsec = 1000 * 100;
+
+		while (nanosleep (&ts, &tsrem) < 0)
+		  ts = tsrem;
+		if (*vlib_worker_threads->wait_at_barrier)
+		  goto done;
+	      }
+	  }
 	goto done;
       }
   }