netdev - Re: [PATCH RFC v8 02/11] vhost: use batched get_vq

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Date:   Tue, 23 Jun 2020 17:54:00 +0200
From:   Eugenio Perez Martin <eperezma@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Jason Wang <jasowang@...hat.com>, linux-kernel@...r.kernel.org,
        kvm list <kvm@...r.kernel.org>,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org
Subject: Re: [PATCH RFC v8 02/11] vhost: use batched get_vq_desc version

On Tue, Jun 23, 2020 at 10:25 AM Michael S. Tsirkin <mst@...hat.com> wrote:
>
> On Tue, Jun 23, 2020 at 09:00:57AM +0200, Eugenio Perez Martin wrote:
> > On Tue, Jun 23, 2020 at 4:51 AM Jason Wang <jasowang@...hat.com> wrote:
> > >
> > >
> > > On 2020/6/23 上午12:00, Michael S. Tsirkin wrote:
> > > > On Wed, Jun 17, 2020 at 11:19:26AM +0800, Jason Wang wrote:
> > > >> On 2020/6/11 下午7:34, Michael S. Tsirkin wrote:
> > > >>>    static void vhost_vq_free_iovecs(struct vhost_virtqueue *vq)
> > > >>>    {
> > > >>>     kfree(vq->descs);
> > > >>> @@ -394,6 +400,9 @@ static long vhost_dev_alloc_iovecs(struct vhost_dev *dev)
> > > >>>     for (i = 0; i < dev->nvqs; ++i) {
> > > >>>             vq = dev->vqs[i];
> > > >>>             vq->max_descs = dev->iov_limit;
> > > >>> +           if (vhost_vq_num_batch_descs(vq) < 0) {
> > > >>> +                   return -EINVAL;
> > > >>> +           }
> > > >> This check breaks vdpa which set iov_limit to zero. Consider iov_limit is
> > > >> meaningless to vDPA, I wonder we can skip the test when device doesn't use
> > > >> worker.
> > > >>
> > > >> Thanks
> > > > It doesn't need iovecs at all, right?
> > > >
> > > > -- MST
> > >
> > >
> > > Yes, so we may choose to bypass the iovecs as well.
> > >
> > > Thanks
> > >
> >
> > I think that the kmalloc_array returns ZERO_SIZE_PTR for all of them
> > in that case, so I didn't bother to skip the kmalloc_array parts.
> > Would you prefer to skip them all and let them NULL? Or have I
> > misunderstood what you mean?
> >
> > Thanks!
>
> Sorry about being unclear. I just meant that it seems cleaner
> to check for iov_limit being 0 not for worker thread.

Actually yes, I also think that iov_limit == 0 is a better check.
Changing for the next revision if everyone agrees.

Thanks!

>
> --
> MST
>