tree b74d1bb2f74384b1a57209bf2d0f453de3968347
parent d3c3589b8b3cd4fabf4cd137facb42a7fb36bd7f
author Paolo Bonzini <pbonzini@redhat.com> 1475746752 +0200
committer Michael S. Tsirkin <mst@redhat.com> 1477866103 +0200

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>