ofproto-dpif-governor: Wake up only when there is genuinely work to do.

Until now, governor_wait() has awakened the poll loop whenever the
generation timer expires, to allow it to shrink the governor to the next
smaller size in governor_run().  However, if the governor is already the
smallest possible size, then governor_run() will not have anything to do
and will not restart the timer, which means that governor_wait() will again
immediately wake up the poll loop, and we end up using 100% CPU.

This is kind of hard to trigger because normally the client will destroy
a governor in such a case.  However, if there are too many subfacets, the
client will keep even a minimum-size governor, triggering the bug.

Bug #12106.
Reported-by: Alex Yip <alex@nicira.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>

diff --git a/ofproto/ofproto-dpif-governor.c b/ofproto/ofproto-dpif-governor.c
index 817186ae52344160f82d5d6292edc7b2e99a54f6..458f8d71f79740aa8346c708e729c5557117805a 100644 (file)
--- a/ofproto/ofproto-dpif-governor.c
+++ b/ofproto/ofproto-dpif-governor.c
@@ -93,7 +93,9 @@ governor_run(struct governor *g)
 void
 governor_wait(struct governor *g)
 {
-    poll_timer_wait_until(g->start + MAX_ELAPSED);
+    if (g->size > MIN_SIZE) {
+        poll_timer_wait_until(g->start + MAX_ELAPSED);
+    }
 }
 
 /* Returns true if 'g' has been doing only a minimal amount of work and thus