linux-kernel - Re: [RFC PATCH 4/4] virtio-net: sleep instead of busy waiting for cvq command

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Message-ID: <CACGkMEvtgr=pDpcZeE4+ssh+PiL0k2B2+3kzdDmEvxxe=2mtGA@mail.gmail.com>
Date:   Fri, 23 Dec 2022 11:00:48 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Alvaro Karsz <alvaro.karsz@...id-run.com>
Cc:     mst@...hat.com, davem@...emloft.net, edumazet@...gle.com,
        kuba@...nel.org, pabeni@...hat.com,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, maxime.coquelin@...hat.com,
        eperezma@...hat.com
Subject: Re: [RFC PATCH 4/4] virtio-net: sleep instead of busy waiting for cvq command

On Thu, Dec 22, 2022 at 11:55 PM Alvaro Karsz
<alvaro.karsz@...id-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