On Fri, Apr 7, 2017 at 5:10 PM, Michael S. Tsirkin <m...@redhat.com> wrote: > On Fri, Apr 07, 2017 at 04:59:58PM -0400, Willem de Bruijn wrote: >> On Fri, Apr 7, 2017 at 3:28 PM, Michael S. Tsirkin <m...@redhat.com> wrote: >> > On Mon, Apr 03, 2017 at 01:02:13AM -0400, Willem de Bruijn wrote: >> >> On Sun, Apr 2, 2017 at 10:47 PM, Michael S. Tsirkin <m...@redhat.com> >> >> wrote: >> >> > On Sun, Apr 02, 2017 at 04:10:12PM -0400, Willem de Bruijn wrote: >> >> >> From: Willem de Bruijn <will...@google.com> >> >> >> >> >> >> Amortize the cost of virtual interrupts by doing both rx and tx work >> >> >> on reception of a receive interrupt if tx napi is enabled. With >> >> >> VIRTIO_F_EVENT_IDX, this suppresses most explicit tx completion >> >> >> interrupts for bidirectional workloads. >> >> >> >> >> >> Signed-off-by: Willem de Bruijn <will...@google.com> >> > >> > This is a popular approach, but I think this will only work well if tx >> > and rx interrupts are processed on the same CPU and if tx queue is per >> > cpu. If they target different CPUs or if tx queue is used from multiple >> > CPUs they will conflict on the shared locks. >> >> Yes. As a result of this discussion I started running a few vcpu affinity >> tests. >> >> > This can even change dynamically as CPUs/queues are reconfigured. >> > How about adding a flag and skipping the tx poll if there's no match? >> >> I suspect that even with the cache invalidations this optimization >> will be an improvement over handling all tx interrupts in the tx napi >> handler. I will get the datapoint for that. >> >> That said, we can make this conditional. What flag exactly do you >> propose? Compare raw_smp_processor_id() in the rx softint with one >> previously stored in the napi tx callback? > > I'm not sure. Another idea is to check vi->affinity_hint_set. > If set we know rq and sq are on the same CPU.
I was not aware of that flag, thanks. Yes, that looks like it should work.
