[ovs-dev] [PATCH 2/2] bridge: Wait for previous stats update transation when it is incomplete.

[Alex Wang]

When ovsdb happens to get blocked for few seconds, the 'stats_timer'
will not be updated due to incompletion of previous transaction.
When the current time passes the 'stats_timer', the call to
poll_timer_wait_until(stats_timer) will keep waking up ovs-vswitchd,
causing 100% cpu utilization.

This commit fixes this issue by making ovs-vswitchd wait on the
previous idl transaction when it is incomplete rather than the
'stats_timer'.

Signed-off-by: Alex Wang <alexw at nicira.com>
---
 vswitchd/bridge.c |   18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/vswitchd/bridge.c b/vswitchd/bridge.c
index 161ba14..cb74aa3 100644
--- a/vswitchd/bridge.c
+++ b/vswitchd/bridge.c
@@ -203,6 +203,8 @@ static bool status_txn_try_again;
  * timeout in 'STATUS_CHECK_AGAIN_MSEC' to check again. */
 #define STATUS_CHECK_AGAIN_MSEC 100
 
+/* Statistics update to database. */
+static struct ovsdb_idl_txn *stats_txn;
 /* Each time this timer expires, the bridge fetches interface and mirror
  * statistics and pushes them into the database. */
 static int stats_timer_interval;
@@ -2693,7 +2695,6 @@ refresh_controller_status(void)
 static void
 run_stats_update(void)
 {
-    static struct ovsdb_idl_txn *stats_txn;
     const struct ovsrec_open_vswitch *cfg = ovsrec_open_vswitch_first(idl);
     int stats_interval;
 
@@ -2748,6 +2749,18 @@ run_stats_update(void)
     }
 }
 
+static void
+stats_update_wait(void)
+{
+    /* If the 'stats_txn' is non-null (transaction incomplete), waits for the
+     * transaction to complete.  Otherwise, waits for the 'stats_timer. */
+    if (stats_txn) {
+        ovsdb_idl_txn_wait(stats_txn);
+    } else {
+        poll_timer_wait_until(stats_timer);
+    }
+}
+
 /* Update bridge/port/interface status if necessary. */
 static void
 run_status_update(void)
@@ -3008,8 +3021,7 @@ bridge_wait(void)
         HMAP_FOR_EACH (br, node, &all_bridges) {
             ofproto_wait(br->ofproto);
         }
-
-        poll_timer_wait_until(stats_timer);
+        stats_update_wait();
         status_update_wait();
     }
 
-- 
1.7.9.5