On Thu, Aug 4, 2022 at 5:14 AM Jason Wang <jasow...@redhat.com> wrote:
>
>
> 在 2022/8/3 01:57, Eugenio Pérez 写道:
> > Since QEMU will be able to inject new elements on CVQ to restore the
> > state, we need not to depend on a VirtQueueElement to know if a new
> > element has been used by the device or not. Instead of check that, check
> > if there are new elements only using used idx on vhost_svq_flush.
> >
> > Signed-off-by: Eugenio Pérez <epere...@redhat.com>
> > ---
> > hw/virtio/vhost-shadow-virtqueue.c | 18 +++++++++---------
> > 1 file changed, 9 insertions(+), 9 deletions(-)
> >
> > diff --git a/hw/virtio/vhost-shadow-virtqueue.c
> > b/hw/virtio/vhost-shadow-virtqueue.c
> > index e6eebd0e8d..fdb550c31b 100644
> > --- a/hw/virtio/vhost-shadow-virtqueue.c
> > +++ b/hw/virtio/vhost-shadow-virtqueue.c
> > @@ -491,7 +491,7 @@ static void vhost_svq_flush(VhostShadowVirtqueue *svq,
> > /**
> > * Poll the SVQ for one device used buffer.
> > *
> > - * This function race with main event loop SVQ polling, so extra
> > + * This function races with main event loop SVQ polling, so extra
> > * synchronization is needed.
> > *
> > * Return the length written by the device.
> > @@ -499,20 +499,20 @@ static void vhost_svq_flush(VhostShadowVirtqueue *svq,
> > size_t vhost_svq_poll(VhostShadowVirtqueue *svq)
> > {
> > int64_t start_us = g_get_monotonic_time();
> > - do {
> > + while (true) {
> > uint32_t len;
> > - VirtQueueElement *elem = vhost_svq_get_buf(svq, &len);
> > - if (elem) {
> > - return len;
> > - }
> >
> > if (unlikely(g_get_monotonic_time() - start_us > 10e6)) {
> > return 0;
> > }
> >
> > - /* Make sure we read new used_idx */
> > - smp_rmb();
> > - } while (true);
> > + if (!vhost_svq_more_used(svq)) {
> > + continue;
> > + }
> > +
> > + vhost_svq_get_buf(svq, &len);
>
>
> I wonder if this means we won't worry about the infinite wait?
>
vhost_svq_get_buf call doesn't block, and the check for the timeout is
immediately above the check for new descriptors. Am I missing
something?
> Thanks
>
>
> > + return len;
> > + }
> > }
> >
> > /**
>
