On Fri, Mar 02, 2018 at 01:38:52PM +0000, Stefan Hajnoczi wrote: > On Tue, Dec 19, 2017 at 1:33 PM, sochin.jiang <sochin.ji...@huawei.com> wrote: > > Till now, we've already notify guest as a batch mostly, an > > extra BH won't decrease guest interrupts much, but cause a > > significant notification loss. Generally, we could have 15% > > or so performance lost in single queue IO models, as I tested. > > Recent performance testing has shown that virtio-blk can underperform > virtio-scsi due to the extra latency added by the BH. > > The virtqueue EVENT_IDX feature mitigates interrupts when the guest > interrupt handler has not had a chance to run yet. Therefore, virtio > already offers one level of interrupt mitigation and the BH adds > additional latency on top.
FWIW, I'm writing a patch that disables the BH (notifying after each completion instead) when EVENT_IDX is present. I'll send both the patch and some fio numbers next week. Sergio.
