netdev - Re: [virtio-dev] Re: [PATCH net-next v1 4/5] virtio_ring: add event idx support in packed ring

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Message-ID: <20180711010905.GB28235@debian>
Date:   Wed, 11 Jul 2018 09:09:05 +0800
From:   Tiwei Bie <tiwei.bie@...el.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     mst@...hat.com, virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        virtio-dev@...ts.oasis-open.org, wexu@...hat.com,
        jfreimann@...hat.com
Subject: Re: [virtio-dev] Re: [PATCH net-next v1 4/5] virtio_ring: add event
 idx support in packed ring

On Tue, Jul 10, 2018 at 01:50:03PM +0800, Jason Wang wrote:
> On 2018年07月09日 15:22, Tiwei Bie wrote:
> > @@ -1059,9 +1059,19 @@ static bool virtqueue_kick_prepare_packed(struct virtqueue *_vq)
> >   	 * suppressions. */
> >   	virtio_mb(vq->weak_barriers);
> > +	old = vq->next_avail_idx - vq->num_added;
> > +	new = vq->next_avail_idx;
> > +	vq->num_added = 0;
> > +
> >   	snapshot = *(u32 *)vq->vring_packed.device;
> 
> I think we should use READ_ONCE() to prevent compiler from re-reading.

I'll do it. Thanks!

Best regards,
Tiwei Bie

> 
> > +	off_wrap = virtio16_to_cpu(_vq->vdev, (__virtio16)(snapshot & 0xffff));
> >   	flags = virtio16_to_cpu(_vq->vdev, (__virtio16)(snapshot >> 16)) & 0x3;
> > +	wrap_counter = off_wrap >> 15;
> > +	event_idx = off_wrap & ~(1 << 15);
> > +	if (wrap_counter != vq->avail_wrap_counter)
> > +		event_idx -= vq->vring_packed.num;
> 
> Thanks
>