dpif-netdev: Trigger parallel pmd reloads.

pmd reloads are currently serialised in each steps calling
reload_affected_pmds.
Any pmd processing packets, waiting on a mutex etc... will make other
pmd threads wait for a delay that can be undeterministic when syscalls
adds up.

Switch to a little busy loop on the control thread using the existing
per-pmd reload boolean.

The memory order on this atomic is rel-acq to have an explicit
synchronisation between the pmd threads and the control thread.

Signed-off-by: David Marchand <david.marchand@redhat.com>
Acked-by: Eelco Chaudron <echaudro@redhat.com>
Acked-by: Ilya Maximets <i.maximets@samsung.com>
Signed-off-by: Ian Stokes <ian.stokes@intel.com>

lib/dpif-netdev.c

@@ -649,9 +649,6 @@ struct dp_netdev_pmd_thread {
     struct ovs_refcount ref_cnt;    /* Every reference must be refcount'ed. */
     struct cmap_node node;          /* In 'dp->poll_threads'. */
 
-    pthread_cond_t cond;            /* For synchronizing pmd thread reload. */
-    struct ovs_mutex cond_mutex;    /* Mutex for condition variable. */
-
     /* Per thread exact-match cache.  Note, the instance for cpu core
      * NON_PMD_CORE_ID can be accessed by multiple threads, and thusly
      * need to be protected by 'non_pmd_mutex'.  Every other instance
@@ -1758,11 +1755,8 @@ dp_netdev_reload_pmd__(struct dp_netdev_pmd_thread *pmd)
         return;
     }
 
-    ovs_mutex_lock(&pmd->cond_mutex);
     seq_change(pmd->reload_seq);
     atomic_store_explicit(&pmd->reload, true, memory_order_release);
-    ovs_mutex_cond_wait(&pmd->cond, &pmd->cond_mutex);
-    ovs_mutex_unlock(&pmd->cond_mutex);
 }
 
 static uint32_t
@@ -4655,6 +4649,19 @@ reload_affected_pmds(struct dp_netdev *dp)
         if (pmd->need_reload) {
             flow_mark_flush(pmd);
             dp_netdev_reload_pmd__(pmd);
+        }
+    }
+
+    CMAP_FOR_EACH (pmd, node, &dp->poll_threads) {
+        if (pmd->need_reload) {
+            if (pmd->core_id != NON_PMD_CORE_ID) {
+                bool reload;
+
+                do {
+                    atomic_read_explicit(&pmd->reload, &reload,
+                                         memory_order_acquire);
+                } while (reload);
+            }
             pmd->need_reload = false;
         }
     }
@@ -5842,11 +5849,8 @@ dpif_netdev_enable_upcall(struct dpif *dpif)
 static void
 dp_netdev_pmd_reload_done(struct dp_netdev_pmd_thread *pmd)
 {
-    ovs_mutex_lock(&pmd->cond_mutex);
-    atomic_store_relaxed(&pmd->reload, false);
     pmd->last_reload_seq = seq_read(pmd->reload_seq);
-    xpthread_cond_signal(&pmd->cond);
-    ovs_mutex_unlock(&pmd->cond_mutex);
+    atomic_store_explicit(&pmd->reload, false, memory_order_release);
 }
 
 /* Finds and refs the dp_netdev_pmd_thread on core 'core_id'.  Returns
@@ -5931,8 +5935,6 @@ dp_netdev_configure_pmd(struct dp_netdev_pmd_thread *pmd, struct dp_netdev *dp,
     pmd->reload_seq = seq_create();
     pmd->last_reload_seq = seq_read(pmd->reload_seq);
     atomic_init(&pmd->reload, false);
-    xpthread_cond_init(&pmd->cond, NULL);
-    ovs_mutex_init(&pmd->cond_mutex);
     ovs_mutex_init(&pmd->flow_mutex);
     ovs_mutex_init(&pmd->port_mutex);
     cmap_init(&pmd->flow_table);
@@ -5975,8 +5977,6 @@ dp_netdev_destroy_pmd(struct dp_netdev_pmd_thread *pmd)
     cmap_destroy(&pmd->flow_table);
     ovs_mutex_destroy(&pmd->flow_mutex);
     seq_destroy(pmd->reload_seq);
-    xpthread_cond_destroy(&pmd->cond);
-    ovs_mutex_destroy(&pmd->cond_mutex);
     ovs_mutex_destroy(&pmd->port_mutex);
     free(pmd);
 }