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From:   Jason Wang <jasowang@redhat.com>
Date:   Mon, 26 Dec 2022 11:45:43 +0800
Message-ID: <CACGkMEs=YrtP-GT_MKoZdORtYCD09QdmZGpgQUHMOMLG_eX-FA@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 Fri, Dec 23, 2022 at 3:39 PM Alvaro Karsz <alvaro.karsz@solid-run.com> wrote:
>
> > 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)
>
> I think that I wasn't clear, sorry.
> I'm not talking about a new virtio feature, I'm talking about a situation when:
> * virtio_net issues a control command.
> * the device gets the command, but somehow, completes the command
> after timeout.
> * virtio_net assumes that the command failed (timeout), and issues a
> different control command.
> * virtio_net will then call virtqueue_wait_for_used, and will
> immediately get the previous response (If I'm not wrong).
>
> So, this is not a new feature that I'm proposing, just a situation
> that may occur due to cvq timeouts.
>
> Anyhow, your solution calling BAD_RING if we reach a timeout should
> prevent this situation.

Right, that is the goal.

Thanks

>
> Thanks
>