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Re: [Qemu-devel] [PATCH v2] hw/virtio/vring/event_idx: fix the vring_ava
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] [PATCH v2] hw/virtio/vring/event_idx: fix the vring_avail_event error |
Date: |
Fri, 31 Oct 2014 10:57:55 +0000 |
User-agent: |
Mutt/1.5.23 (2014-03-12) |
On Fri, Oct 31, 2014 at 12:40:16AM +0000, Bin Wu wrote:
> The event idx in virtio is an effective way to reduce the number of
> interrupts and exits of the guest. When the guest puts an request
> into the virtio ring, it doesn't exit immediately to inform the
> backend. Instead, the guest checks the "avail" event idx to determine
> the notification.
>
> In virtqueue_pop, when a request is poped, the current avail event
> idx should be set to the number of vq->last_avail_idx.
>
> Signed-off-by: Bin Wu <address@hidden>
> ---
> V2 -> V1:
> update the same code in hw/virtio/dataplane/vring.c (Stefan)
> ---
> hw/virtio/dataplane/vring.c | 8 ++++----
> hw/virtio/virtio.c | 2 +-
> 2 files changed, 5 insertions(+), 5 deletions(-)
Reviewed-by: Stefan Hajnoczi <address@hidden>
By the way, did you see that kernel drivers/vhost/vhost.c doesn't update
the field for each pop? Instead it only updates when notify is
re-enabled. I wonder if that approach is better than what QEMU does.
Stefan
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