bfd/cfm: Check status change before update status to database.

This commit adds boolean flag in bfd/cfm module for checking
status change.  If there is no status change, the current
update to OVS database will skip the bfd/cfm session.

In the experiment with 5K bfd sessions, when one session is
flapping at rate of every 0.3 second, this patch reduces the
cpu utilization of the ovs-vswitchd thread from 13 to 6.

Signed-off-by: Alex Wang <alexw@nicira.com>
Acked-by: Joe Stringer <joestringer@nicira.com>

1 files changed, 30 insertions, 2 deletions

diff --git a/lib/cfm.c b/lib/cfm.c
index ce0c471e3..6a173a709 100644
--- a/lib/cfm.c
+++ b/lib/cfm.c
@@ -133,6 +133,10 @@ struct cfm {
     struct ovs_refcount ref_cnt;
 
     uint64_t flap_count;       /* Count the flaps since boot. */
+
+    /* True when the variables returned by cfm_get_*() are changed
+     * since last check. */
+    bool status_changed;
 };
 
 /* Remote MPs represent foreign network entities that are configured to have
@@ -343,6 +347,7 @@ cfm_create(const struct netdev *netdev) OVS_EXCLUDED(mutex)
     cfm_generate_maid(cfm);
     hmap_insert(all_cfms, &cfm->hmap_node, hash_string(cfm->name, 0));
     ovs_mutex_unlock(&mutex);
+
     return cfm;
 }
 
@@ -385,6 +390,14 @@ cfm_ref(const struct cfm *cfm_)
     return cfm;
 }
 
+/* Records the status change and changes the global connectivity seq. */
+static void
+cfm_status_changed(struct cfm *cfm) OVS_REQUIRES(mutex)
+{
+    seq_change(connectivity_seq_get());
+    cfm->status_changed = true;
+}
+
 /* Should be run periodically to update fault statistics messages. */
 void
 cfm_run(struct cfm *cfm) OVS_EXCLUDED(mutex)
@@ -510,7 +523,7 @@ cfm_run(struct cfm *cfm) OVS_EXCLUDED(mutex)
             || (old_rmps_array_len != cfm->rmps_array_len || old_rmps_deleted)
             || old_cfm_fault != cfm->fault
             || old_flap_count != cfm->flap_count) {
-            seq_change(connectivity_seq_get());
+            cfm_status_changed(cfm);
         }
 
         cfm->booted = true;
@@ -836,6 +849,20 @@ out:
     ovs_mutex_unlock(&mutex);
 }
 
+/* Returns and resets the 'cfm->status_changed'. */
+bool
+cfm_check_status_change(struct cfm *cfm) OVS_EXCLUDED(mutex)
+{
+    bool ret;
+
+    ovs_mutex_lock(&mutex);
+    ret = cfm->status_changed;
+    cfm->status_changed = false;
+    ovs_mutex_unlock(&mutex);
+
+    return ret;
+}
+
 static int
 cfm_get_fault__(const struct cfm *cfm) OVS_REQUIRES(mutex)
 {
@@ -1029,13 +1056,14 @@ cfm_unixctl_set_fault(struct unixctl_conn *conn, int argc, const char *argv[],
             goto out;
         }
         cfm->fault_override = fault_override;
+        cfm_status_changed(cfm);
     } else {
         HMAP_FOR_EACH (cfm, hmap_node, all_cfms) {
             cfm->fault_override = fault_override;
+            cfm_status_changed(cfm);
         }
     }
 
-    seq_change(connectivity_seq_get());
     unixctl_command_reply(conn, "OK");
 
 out: