Alvaro Karsz
2022-Dec-22 06:44 UTC
[RFC PATCH 4/4] virtio-net: sleep instead of busy waiting for cvq command
Hi Jason, Adding timeout to the cvq is a great idea IMO.> - /* Spin for a response, the kick causes an ioport write, trapping > - * into the hypervisor, so the request should be handled immediately. > - */ > - while (!virtqueue_get_buf(vi->cvq, &tmp) && > - !virtqueue_is_broken(vi->cvq)) > - cpu_relax(); > + virtqueue_wait_for_used(vi->cvq, &tmp);Do you think that we should continue like nothing happened in case of a timeout? Shouldn't we reset the device? What happens if a device completes the control command after timeout? Thanks Alvaro
Jason Wang
2022-Dec-22 08:43 UTC
[RFC PATCH 4/4] virtio-net: sleep instead of busy waiting for cvq command
Hi Alvaro: On Thu, Dec 22, 2022 at 2:44 PM Alvaro Karsz <alvaro.karsz at solid-run.com> wrote:> > Hi Jason, > > Adding timeout to the cvq is a great idea IMO. > > > - /* Spin for a response, the kick causes an ioport write, trapping > > - * into the hypervisor, so the request should be handled immediately. > > - */ > > - while (!virtqueue_get_buf(vi->cvq, &tmp) && > > - !virtqueue_is_broken(vi->cvq)) > > - cpu_relax(); > > + virtqueue_wait_for_used(vi->cvq, &tmp); > > Do you think that we should continue like nothing happened in case of a timeout?We could, but we should not depend on a device to do this since it's not reliable. More below.> Shouldn't we reset the device?We can't depend on device, there's probably another loop in reset(): E.g in vp_reset() we had: while (vp_modern_get_status(mdev)) msleep(1);> What happens if a device completes the control command after timeout?Maybe we could have a BAD_RING() here in this case (and more check in vq->broken in this case). Thanks> > Thanks > > Alvaro >