On Mon, Jul 11, 2022 at 11:19 AM Jason Wang <jasow...@redhat.com> wrote:
>
>
> 在 2022/7/7 02:39, Eugenio Pérez 写道:
> > It allows the Shadow Control VirtQueue to wait the device to use the
> > commands
> > that restore the net device state after a live migration.
> >
> > Signed-off-by: Eugenio Pérez <epere...@redhat.com>
> > ---
> > hw/virtio/vhost-shadow-virtqueue.h | 1 +
> > hw/virtio/vhost-shadow-virtqueue.c | 54 ++++++++++++++++++++++++++++--
> > 2 files changed, 52 insertions(+), 3 deletions(-)
> >
> > diff --git a/hw/virtio/vhost-shadow-virtqueue.h
> > b/hw/virtio/vhost-shadow-virtqueue.h
> > index d01d2370db..c8668fbdd6 100644
> > --- a/hw/virtio/vhost-shadow-virtqueue.h
> > +++ b/hw/virtio/vhost-shadow-virtqueue.h
> > @@ -100,6 +100,7 @@ void vhost_svq_push_elem(VhostShadowVirtqueue *svq,
> > const VirtQueueElement *elem, uint32_t len);
> > int vhost_svq_inject(VhostShadowVirtqueue *svq, const struct iovec *iov,
> > size_t out_num, size_t in_num, void *opaque);
> > +ssize_t vhost_svq_poll(VhostShadowVirtqueue *svq);
> > void vhost_svq_set_svq_kick_fd(VhostShadowVirtqueue *svq, int
> > svq_kick_fd);
> > void vhost_svq_set_svq_call_fd(VhostShadowVirtqueue *svq, int call_fd);
> > void vhost_svq_get_vring_addr(const VhostShadowVirtqueue *svq,
> > diff --git a/hw/virtio/vhost-shadow-virtqueue.c
> > b/hw/virtio/vhost-shadow-virtqueue.c
> > index bd9e34b413..ed7f1d0bc9 100644
> > --- a/hw/virtio/vhost-shadow-virtqueue.c
> > +++ b/hw/virtio/vhost-shadow-virtqueue.c
> > @@ -10,6 +10,8 @@
> > #include "qemu/osdep.h"
> > #include "hw/virtio/vhost-shadow-virtqueue.h"
> >
> > +#include <glib/gpoll.h>
> > +
> > #include "qemu/error-report.h"
> > #include "qapi/error.h"
> > #include "qemu/main-loop.h"
> > @@ -490,10 +492,11 @@ void vhost_svq_push_elem(VhostShadowVirtqueue *svq,
> > }
> > }
> >
> > -static void vhost_svq_flush(VhostShadowVirtqueue *svq,
> > - bool check_for_avail_queue)
> > +static size_t vhost_svq_flush(VhostShadowVirtqueue *svq,
> > + bool check_for_avail_queue)
> > {
> > VirtQueue *vq = svq->vq;
> > + size_t ret = 0;
> >
> > /* Forward as many used buffers as possible. */
> > do {
> > @@ -510,7 +513,7 @@ static void vhost_svq_flush(VhostShadowVirtqueue *svq,
> > "More than %u used buffers obtained in a %u size
> > SVQ",
> > i, svq->vring.num);
> > virtqueue_flush(vq, svq->vring.num);
> > - return;
> > + return ret;
> > }
> >
> > svq_elem = vhost_svq_get_buf(svq, &len);
> > @@ -520,6 +523,7 @@ static void vhost_svq_flush(VhostShadowVirtqueue *svq,
> >
> > elem = g_steal_pointer(&svq_elem.opaque);
> > virtqueue_fill(vq, elem, len, i++);
> > + ret++;
> > }
> >
> > virtqueue_flush(vq, i);
> > @@ -533,6 +537,50 @@ static void vhost_svq_flush(VhostShadowVirtqueue *svq,
> > vhost_handle_guest_kick(svq);
> > }
> > } while (!vhost_svq_enable_notification(svq));
> > +
> > + return ret;
> > +}
> > +
> > +/**
> > + * Poll the SVQ for device used buffers.
> > + *
> > + * This function race with main event loop SVQ polling, so extra
> > + * synchronization is needed.
> > + *
> > + * Return the number of descriptors read from the device.
> > + */
> > +ssize_t vhost_svq_poll(VhostShadowVirtqueue *svq)
> > +{
> > + int fd = event_notifier_get_fd(&svq->hdev_call);
> > + GPollFD poll_fd = {
> > + .fd = fd,
> > + .events = G_IO_IN,
> > + };
> > + assert(fd >= 0);
> > + int r = g_poll(&poll_fd, 1, -1);
>
>
> Any reason we can't simply (busy) polling the used ring here? It might
> help to reduce the latency (and it is what kernel driver uses).
>
Yes, I'll change to a busy polling. I forgot to change it.
Thanks!
> Thanks
>
>
> > +
> > + if (unlikely(r < 0)) {
> > + error_report("Cannot poll device call fd "G_POLLFD_FORMAT": (%d)
> > %s",
> > + poll_fd.fd, errno, g_strerror(errno));
> > + return -errno;
> > + }
> > +
> > + if (r == 0) {
> > + return 0;
> > + }
> > +
> > + if (unlikely(poll_fd.revents & ~(G_IO_IN))) {
> > + error_report(
> > + "Error polling device call fd "G_POLLFD_FORMAT": revents=%d",
> > + poll_fd.fd, poll_fd.revents);
> > + return -1;
> > + }
> > +
> > + /*
> > + * Max return value of vhost_svq_flush is (uint16_t)-1, so it's safe to
> > + * convert to ssize_t.
> > + */
> > + return vhost_svq_flush(svq, false);
> > }
> >
> > /**
>
