From 948a8ac2964f39161ebf832dea0aa1ced90101bb Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Thu, 6 Oct 2016 11:39:12 +0200 Subject: [PATCH] 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 Signed-off-by: Michael S. Tsirkin --- tools/virtio/ringtest/main.c | 4 ++-- 1 file 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(); -- 2.20.1