From: Florin Coras <fcoras@cisco.com>
Date: Wed, 30 Mar 2022 20:50:19 +0000 (-0700)
Subject: vlib: add support for workers sync
X-Git-Tag: v22.10-rc0~163
X-Git-Url: https://gerrit.fd.io/r/gitweb?a=commitdiff_plain;h=4b20830b496ade3f1e77cd5fcbdf6d6c7bb5336d;p=vpp.git

vlib: add support for workers sync

Adds api that allows workers to synchronize through main thread.

Type: improvement

Signed-off-by: Florin Coras <fcoras@cisco.com>
Change-Id: I1e75e2fb5144d397d19b13c4dfc7e937f11c044c
---

diff --git a/src/vlib/threads.c b/src/vlib/threads.c
index b470976d3d3..e34ef7c30cb 100644
--- a/src/vlib/threads.c
+++ b/src/vlib/threads.c
@@ -1480,6 +1480,56 @@ vlib_worker_thread_barrier_release (vlib_main_t * vm)
 			 vm->clib_time.last_cpu_time, 1 /* leave */ );
 }
 
+static void
+vlib_worker_sync_rpc (void *args)
+{
+  ASSERT (vlib_thread_is_main_w_barrier ());
+  vlib_worker_threads->wait_before_barrier = 0;
+}
+
+void
+vlib_workers_sync (void)
+{
+  if (PREDICT_FALSE (!vlib_num_workers ()))
+    return;
+
+  if (!(*vlib_worker_threads->wait_at_barrier) &&
+      !clib_atomic_swap_rel_n (&vlib_worker_threads->wait_before_barrier, 1))
+    {
+      u32 thread_index = vlib_get_thread_index ();
+      vlib_rpc_call_main_thread (vlib_worker_sync_rpc, (u8 *) &thread_index,
+				 sizeof (thread_index));
+    }
+
+  /* Wait until main thread asks for barrier */
+  while (!(*vlib_worker_threads->wait_at_barrier))
+    ;
+
+  /* Stop before barrier and make sure all threads are either
+   * at worker barrier or the barrier before it */
+  clib_atomic_fetch_add (&vlib_worker_threads->workers_before_barrier, 1);
+  while (vlib_num_workers () > (*vlib_worker_threads->workers_at_barrier +
+				vlib_worker_threads->workers_before_barrier))
+    ;
+}
+
+void
+vlib_workers_continue (void)
+{
+  if (PREDICT_FALSE (!vlib_num_workers ()))
+    return;
+
+  clib_atomic_fetch_add (&vlib_worker_threads->done_work_before_barrier, 1);
+
+  /* Wait until all workers are done with work before barrier */
+  while (vlib_worker_threads->done_work_before_barrier <
+	 vlib_worker_threads->workers_before_barrier)
+    ;
+
+  clib_atomic_fetch_add (&vlib_worker_threads->done_work_before_barrier, -1);
+  clib_atomic_fetch_add (&vlib_worker_threads->workers_before_barrier, -1);
+}
+
 /**
  * Wait until each of the workers has been once around the track
  */
diff --git a/src/vlib/threads.h b/src/vlib/threads.h
index e406dde5b07..b25d4764168 100644
--- a/src/vlib/threads.h
+++ b/src/vlib/threads.h
@@ -101,6 +101,9 @@ typedef struct
   const char *barrier_caller;
   const char *barrier_context;
   volatile u32 *node_reforks_required;
+  volatile u32 wait_before_barrier;
+  volatile u32 workers_before_barrier;
+  volatile u32 done_work_before_barrier;
 
   long lwp;
   int cpu_id;
@@ -484,6 +487,17 @@ void vlib_rpc_call_main_thread (void *function, u8 * args, u32 size);
 void vlib_get_thread_core_numa (vlib_worker_thread_t * w, unsigned cpu_id);
 vlib_thread_main_t *vlib_get_thread_main_not_inline (void);
 
+/**
+ * Force workers sync from within worker
+ *
+ * Must be paired with @ref vlib_workers_continue
+ */
+void vlib_workers_sync (void);
+/**
+ * Release barrier after workers sync
+ */
+void vlib_workers_continue (void);
+
 #endif /* included_vlib_threads_h */
 
 /*
diff --git a/src/vnet/session/session.h b/src/vnet/session/session.h
index 56e30e6533b..0cf6cd084fe 100644
--- a/src/vnet/session/session.h
+++ b/src/vnet/session/session.h
@@ -803,41 +803,6 @@ pool_program_safe_realloc (void *p, u32 thread_index,
 				  uword_to_pointer (thread_index, void *));
 }
 
-#define pool_realloc_all_at_barrier(_not)                                     \
-  (*vlib_worker_threads->workers_at_barrier >= (vlib_num_workers () - _not))
-
-always_inline void
-pool_realloc_wait_at_barrier (void)
-{
-  session_main_t *sm = &session_main;
-
-  /* Wait until main thread asks for barrier */
-  while (!(*vlib_worker_threads->wait_at_barrier))
-    ;
-
-  /* Stop at realloc barrier and make sure all threads are either
-   * at worker barrier or at pool realloc barrier */
-  clib_atomic_fetch_add (&sm->pool_realloc_at_barrier, 1);
-  while (!pool_realloc_all_at_barrier (sm->pool_realloc_at_barrier))
-    ;
-
-  /* Track all workers that are doing work */
-  clib_atomic_fetch_add (&sm->pool_realloc_doing_work, 1);
-}
-
-always_inline void
-pool_realloc_done_wait_at_barrier (void)
-{
-  session_main_t *sm = &session_main;
-
-  /* Wait until all workers at pool realloc barrier have started reallocs */
-  while (sm->pool_realloc_doing_work < sm->pool_realloc_at_barrier)
-    ;
-
-  clib_atomic_fetch_add (&sm->pool_realloc_doing_work, -1);
-  clib_atomic_fetch_add (&sm->pool_realloc_at_barrier, -1);
-}
-
 #define pool_needs_realloc(P)                                                 \
   ((!P) ||                                                                    \
    (vec_len (pool_header (P)->free_indices) < POOL_REALLOC_SAFE_ELT_THRESH && \
@@ -857,10 +822,9 @@ pool_realloc_done_wait_at_barrier (void)
 	    }                                                                 \
 	  else if (PREDICT_FALSE (!pool_free_elts (P)))                       \
 	    {                                                                 \
-	      pool_program_safe_realloc (P, thread_index, rpc_fn);            \
-	      pool_realloc_wait_at_barrier ();                                \
+	      vlib_workers_sync ();                                           \
 	      pool_alloc_aligned (P, pool_max_len (P), align);                \
-	      pool_realloc_done_wait_at_barrier ();                           \
+	      vlib_workers_continue ();                                       \
 	      ALWAYS_ASSERT (pool_free_elts (P) > 0);                         \
 	    }                                                                 \
 	  else                                                                \