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From:   Jason Wang <jasowang@redhat.com>
Date:   Fri, 23 Dec 2022 11:00:48 +0800
Message-ID: <CACGkMEvtgr=pDpcZeE4+ssh+PiL0k2B2+3kzdDmEvxxe=2mtGA@mail.gmail.com>
Subject: Re: [RFC PATCH 4/4] virtio-net: sleep instead of busy waiting for cvq command
To:     Alvaro Karsz <alvaro.karsz@solid-run.com>
Cc:     mst@redhat.com, davem@davemloft.net, edumazet@google.com,
        kuba@kernel.org, pabeni@redhat.com,
        virtualization@lists.linux-foundation.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, maxime.coquelin@redhat.com,
        eperezma@redhat.com
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On Thu, Dec 22, 2022 at 11:55 PM Alvaro Karsz
<alvaro.karsz@solid-run.com> wrote:
>
> My point is that the device may complete the control command after the timeout,

This needs to be proposed to the virtio spec first. And actually we
need more than this:

1) we still need a way to deal with the device without this feature
2) driver can't depend solely on what is advertised by the device (e.g
device can choose to advertise a very long timeout)

> so, if I'm not mistaken, next time we send a control command and call
> virtqueue_wait_for_used we'll get the previous response.
>

In the next version, I will first put BAD_RING() to prevent future
requests for cvq.

Note that the patch can't fix all the issues, we need more things on
top. But it's a good step and it will behave much better than the
current code.

Thanks