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authorPaolo Bonzini <pbonzini@redhat.com>2016-10-06 11:39:12 +0200
committerMichael S. Tsirkin <mst@redhat.com>2016-10-31 00:21:43 +0200
commit948a8ac2964f39161ebf832dea0aa1ced90101bb (patch)
treeb74d1bb2f74384b1a57209bf2d0f453de3968347
parentd3c3589b8b3cd4fabf4cd137facb42a7fb36bd7f (diff)
ringtest: poll for new buffers once before updating event index
Updating the event index has a memory barrier and causes more work on the other side to actually signal the event. It is unnecessary if a new buffer has already appeared on the ring, so poll once before doing the update. The effect of this on the 0.9 ring implementation is pretty much invisible, but on the new-style ring it provides a consistent 3% performance improvement. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
-rw-r--r--tools/virtio/ringtest/main.c4
1 files changed, 2 insertions, 2 deletions
diff --git a/tools/virtio/ringtest/main.c b/tools/virtio/ringtest/main.c
index b00ecd619969..f31353fac541 100644
--- a/tools/virtio/ringtest/main.c
+++ b/tools/virtio/ringtest/main.c
@@ -147,7 +147,7 @@ static void __attribute__((__flatten__)) run_guest(void)
assert(completed <= bufs);
assert(started <= bufs);
if (do_sleep) {
- if (enable_call())
+ if (used_empty() && enable_call())
wait_for_call();
} else {
poll_used();
@@ -172,7 +172,7 @@ static void __attribute__((__flatten__)) run_host(void)
for (;;) {
if (do_sleep) {
- if (enable_kick())
+ if (avail_empty() && enable_kick())
wait_for_kick();
} else {
poll_avail();