[ovs-dev] [PATCH v3 2/5] dpif-netdev: Trigger parallel pmd reloads.

[David Marchand]

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 at redhat.com>
---
Changelog since v2:
- remove unneeded synchronisation on pmd thread join (Ilya)
- "inlined" synchronisation loop in reload_affected_pmds

Changelog since v1:
- removed the introduced reloading_pmds atomic and reuse the existing
  pmd->reload boolean as a single synchronisation point (Ilya)

Changelog since RFC v1:
- added memory ordering on 'reloading_pmds' atomic to serve as a
  synchronisation point between pmd threads and control thread

---
 lib/dpif-netdev.c | 26 ++++++++++++--------------
 1 file changed, 12 insertions(+), 14 deletions(-)

diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c
index 8eeec63..415107b 100644
--- a/lib/dpif-netdev.c
+++ b/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 +4649,17 @@ 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) {
+            bool reload;
+
+            do {
+                atomic_read_explicit(&pmd->reload, &reload,
+                                     memory_order_acquire);
+            } while (reload);
             pmd->need_reload = false;
         }
     }
@@ -5842,11 +5847,8 @@ 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 +5933,6 @@ 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 +5975,6 @@ 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);
 }
-- 
1.8.3.1