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

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Message-ID: <20200623042456-mutt-send-email-mst@kernel.org>
Date:   Tue, 23 Jun 2020 04:25:46 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Eugenio Perez Martin <eperezma@...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 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.

-- 
MST