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

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Message-ID: <6715f515-3db6-1006-09dd-19464e3ff676@redhat.com>
Date:   Tue, 23 Jun 2020 15:15:40 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Eugenio Perez Martin <eperezma@...hat.com>
Cc:     "Michael S. Tsirkin" <mst@...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 2020/6/23 下午3:00, 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?


I'm ok with either approach, but my understanding is that Michael wants 
to skip them all.

Thanks


>
> Thanks!
>