[ovs-dev] [PATCHv5 4/4] bridge: Only store instant_stats on device changes

[Joe Stringer]

Previously, we iterated through all interfaces in instant_stats_run(),
grabbing up-to-date information about device and port status. After
assembling all of this information for all interfaces, we would
determine whether anything changed and only send an update to
ovsdb-server if something changed.

This patch uses the new global connectivity_seq to determine whether
there have been any changes before polling all interfaces, which reduces
unnecessary processing in the average case. In a test environment of
5000 internal ports and 50 tunnel ports with bfd, this reduces average
CPU usage of the main thread from about 15% to about 5%. When ports
change status more often than every 100ms, CPU usage is expected to
increase to previous rates.

Signed-off-by: Joe Stringer <joestringer at nicira.com>
Acked-by: Ethan Jackson <ethan at nicira.com>
---
v5: Rebase
    Tweak commit message
---
 vswitchd/bridge.c |   12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/vswitchd/bridge.c b/vswitchd/bridge.c
index f3b03af..eb63105 100644
--- a/vswitchd/bridge.c
+++ b/vswitchd/bridge.c
@@ -22,6 +22,7 @@
 #include "bfd.h"
 #include "bitmap.h"
 #include "cfm.h"
+#include "connectivity.h"
 #include "coverage.h"
 #include "daemon.h"
 #include "dirs.h"
@@ -41,6 +42,7 @@
 #include "ofproto/bond.h"
 #include "ofproto/ofproto.h"
 #include "poll-loop.h"
+#include "seq.h"
 #include "sha1.h"
 #include "shash.h"
 #include "smap.h"
@@ -155,6 +157,9 @@ static struct ovsdb_idl_txn *daemonize_txn;
 /* Most recently processed IDL sequence number. */
 static unsigned int idl_seqno;
 
+/* Track changes to port connectivity. */
+static uint64_t connectivity_seqno = LLONG_MIN;
+
 /* Each time this timer expires, the bridge fetches interface and mirror
  * statistics and pushes them into the database. */
 #define IFACE_STATS_INTERVAL (5 * 1000) /* In milliseconds. */
@@ -2164,12 +2169,19 @@ instant_stats_run(void)
 
     if (!instant_txn) {
         struct bridge *br;
+        uint64_t seq;
 
         if (time_msec() < instant_next_txn) {
             return;
         }
         instant_next_txn = time_msec() + INSTANT_INTERVAL_MSEC;
 
+        seq = seq_read(connectivity_seq_get());
+        if (seq == connectivity_seqno) {
+            return;
+        }
+        connectivity_seqno = seq;
+
         instant_txn = ovsdb_idl_txn_create(idl);
         HMAP_FOR_EACH (br, node, &all_bridges) {
             struct iface *iface;
-- 
1.7.9.5