On Mon, Apr 04, 2016 at 03:57:11PM -0700, Rich Lane wrote:
> On Mon, Apr 4, 2016 at 1:05 PM, Yuanhan Liu <yuanhan.liu at linux.intel.com>
> wrote:
>
> On Mon, Apr 04, 2016 at 03:13:37PM +0200, Thomas Monjalon wrote:
> > Huawei, Yuanhan, any comment?
> >
> > 2016-03-31 13:01, Rich Lane:
> > >? ? ? ? ? ? ? ? ? ? ? ? ? ? ?vq->vq_ring.desc[i + mid_idx].next = i;
> > >? ? ? ? ? ? ? ? ? ? ? ? ? ? ?vq->vq_ring.desc[i + mid_idx].addr =
> > > -? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?vq->virtio_net_hdr_mem +
> > > -? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?i *
> vq->hw->vtnet_hdr_size;
> > > +? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?vq->virtio_net_hdr_mem;
>
> I could be wrong, but this looks like a special case when i == 0,
> which is by no way that zeroed memory is guaranteed? Huawei, do
> you have time to check this patch??
>
>
> This bug exists because the type of the objects pointed to by
> virtio_net_hdr_mem changed in 6dc5de3a (virtio: use indirect ring elements),
> but because it isn't a C pointer the compiler didn't?catch the type mismatch.
> We could also fix it with:
>
> ? ? vq->virtio_net_hdr_mem + i * sizeof(struct virtio_tx_region) + offsetof
> (struct virtio_tx_region, tx_hdr)
>
> Given that tx_hdr is the first member in struct virtio_tx_region, and using a
> single header optimizes cache use, that simplifies to the code in my patch.
It does. However, it hurts readability.
> The
> virtio-net header is never written to by simple TX so it remains zeroed.
>
> I can respin the patch using offsetof if that's preferred.
Yes, please. In such way, we could also align with the setting up code
at virtio_dev_queue_setup().
BTW, I have one question: will simple Tx work with indirect buf
enabled?
> Note that right now virtio simple TX is broken with DPDK vhost due to the
> flood
> of error messages.
Yes, we need the fix, and thanks for the catching. BTW, it's a
regression fix, you'd better add a Fixline into your commit log.
--yliu
