On Wed, Dec 11, 2019 at 10:58:43AM -0500, Michael S. Tsirkin wrote: > On Mon, Dec 09, 2019 at 09:09:57PM +0000, Stefan Hajnoczi wrote: > > Virtqueue notifications are not necessary during polling, so we disable > > them. This allows the guest driver to avoid MMIO vmexits. > > Unfortunately the virtio-blk and virtio-scsi handler functions re-enable > > notifications, defeating this optimization. > > > > Fix virtio-blk and virtio-scsi emulation so they leave notifications > > disabled. The key thing to remember for correctness is that polling > > always checks one last time after ending its loop, therefore it's safe > > to lose the race when re-enabling notifications at the end of polling. > > > > There is a measurable performance improvement of 5-10% with the null-co > > block driver. Real-life storage configurations will see a smaller > > improvement because the MMIO vmexit overhead contributes less to > > latency. > > > > Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com> > > > Thanks! I'll queue it for merge after the release. If possible please ping me > after the release to help make sure it didn't get dropped.
Great, thanks! Stefan
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