[dpdk-dev] [PATCH] virtio: fix the vq size issue

[Ouyang, Changchun]

> -----Original Message-----
> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Thomas Monjalon
> Sent: Friday, July 10, 2015 10:12 PM
> To: Xie, Huawei
> Cc: dev at dpdk.org
> Subject: Re: [dpdk-dev] [PATCH] virtio: fix the vq size issue
> 
> 2015-07-10 14:05, Xie, Huawei:
> > Thomas:
> > Could we roll back that commit or apply Changchun's patch?
> 
> It is waiting an agreement with Changchun, symbolized by an Acked-by:

I think applying this patch is better than rolling back the previous commit,
Besides fixing the issue, this patch also removes an unnecessary assigning inside that function.

> 
> 
> > On 7/1/2015 11:53 PM, Xie, Huawei wrote:
> > > On 7/1/2015 3:49 PM, Ouyang Changchun wrote:
> > >> This commit breaks virtio basic packets rx functionality:
> > >>   d78deadae4dca240e85054bf2d604a801676becc
> > >>
> > >> The QEMU use 256 as default vring size, also use this default value
> > >> to calculate the virtio avail ring base address and used ring base
> > >> address, and vhost in the backend use the ring base address to do
> packet IO.
> > >>
> > >> Virtio spec also says the queue size in PCI configuration is
> > >> read-only, so virtio front end can't change it. just need use the
> > >> read-only value to allocate space for vring and calculate the avail
> > >> and used ring base address. Otherwise, the avail and used ring base
> address will be different between host and guest, accordingly, packet IO
> can't work normally.
> > > virtio driver could still use the vq_size to initialize avail ring
> > > and use ring so that they still have the same base address.
> > > The other issue is vhost use  index & (vq->size -1) to index the ring.
> > >
> > >
> > > Thomas:
> > > This fix works but introduces slight change with original code.
> > > Could we just rollback that commit?
> > >
> > > d78deadae4dca240e85054bf2d604a801676becc
> > >
> > >
> > >> Signed-off-by: Changchun Ouyang <changchun.ouyang at intel.com>
> > >> ---
> > >>  drivers/net/virtio/virtio_ethdev.c | 14 +++-----------
> > >>  1 file changed, 3 insertions(+), 11 deletions(-)