[ovs-dev,RFC,v2,2/5] dpif-netdev: Trigger parallel pmd reloads.
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Message ID 1557851610-5602-3-git-send-email-david.marchand@redhat.com
State Superseded
Headers show
Series
  • Quicker pmd threads reloads
Related show

Commit Message

David Marchand May 14, 2019, 4:33 p.m. UTC
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 an atomic
count.

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>
---
 lib/dpif-netdev.c | 50 +++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 37 insertions(+), 13 deletions(-)

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

Patch
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diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c
index 37366e2..4febd8b 100644
--- a/lib/dpif-netdev.c
+++ b/lib/dpif-netdev.c
@@ -335,6 +335,9 @@  struct dp_netdev {
     /* The time that a packet can wait in output batch for sending. */
     atomic_uint32_t tx_flush_interval;
 
+    /* Count of pmds currently reloading */
+    atomic_uint32_t reloading_pmds;
+
     /* Meters. */
     struct ovs_mutex meter_locks[N_METER_LOCKS];
     struct dp_meter *meters[MAX_METERS]; /* Meter bands. */
@@ -647,9 +650,6 @@  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
@@ -1525,6 +1525,8 @@  create_dp_netdev(const char *name, const struct dpif_class *class,
     atomic_init(&dp->emc_insert_min, DEFAULT_EM_FLOW_INSERT_MIN);
     atomic_init(&dp->tx_flush_interval, DEFAULT_TX_FLUSH_INTERVAL);
 
+    atomic_init(&dp->reloading_pmds, 0);
+
     cmap_init(&dp->poll_threads);
     dp->pmd_rxq_assign_cyc = true;
 
@@ -1754,11 +1756,8 @@  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
@@ -4641,9 +4640,31 @@  rxq_scheduling(struct dp_netdev *dp, bool pinned) OVS_REQUIRES(dp->port_mutex)
 }
 
 static void
+wait_reloading_pmds(struct dp_netdev *dp)
+{
+    uint32_t reloading;
+
+    do {
+        atomic_read_explicit(&dp->reloading_pmds, &reloading,
+                             memory_order_acquire);
+    } while (reloading != 0);
+}
+
+static void
 reload_affected_pmds(struct dp_netdev *dp)
 {
     struct dp_netdev_pmd_thread *pmd;
+    unsigned int pmd_count = 0;
+
+    CMAP_FOR_EACH (pmd, node, &dp->poll_threads) {
+        if (pmd->core_id == NON_PMD_CORE_ID) {
+            continue;
+        }
+        if (pmd->need_reload) {
+            pmd_count++;
+        }
+    }
+    atomic_store_relaxed(&dp->reloading_pmds, pmd_count);
 
     CMAP_FOR_EACH (pmd, node, &dp->poll_threads) {
         if (pmd->need_reload) {
@@ -4652,6 +4673,10 @@  reload_affected_pmds(struct dp_netdev *dp)
             pmd->need_reload = false;
         }
     }
+
+    if (pmd_count != 0) {
+        wait_reloading_pmds(dp);
+    }
 }
 
 static void
@@ -5813,11 +5838,12 @@  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);
+    uint32_t old;
+
     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_sub_explicit(&pmd->dp->reloading_pmds, 1, &old,
+                        memory_order_release);
 }
 
 /* Finds and refs the dp_netdev_pmd_thread on core 'core_id'.  Returns
@@ -5902,8 +5928,6 @@  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);
@@ -5946,8 +5970,6 @@  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);
 }
@@ -5967,7 +5989,9 @@  dp_netdev_del_pmd(struct dp_netdev *dp, struct dp_netdev_pmd_thread *pmd)
         ovs_mutex_unlock(&dp->non_pmd_mutex);
     } else {
         atomic_store_relaxed(&pmd->exit, true);
+        atomic_store_relaxed(&dp->reloading_pmds, 1);
         dp_netdev_reload_pmd__(pmd);
+        wait_reloading_pmds(dp);
         xpthread_join(pmd->thread, NULL);
     }