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

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Message-ID: <CAJs=3_D6sug80Bb9tnAw5T0_NaL_b=u8ZMcwZtd-dy+AH_yqzQ@mail.gmail.com>
Date:   Thu, 22 Dec 2022 08:44:12 +0200
From:   Alvaro Karsz <alvaro.karsz@...id-run.com>
To:     Jason Wang <jasowang@...hat.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

Hi Jason,

Adding timeout to the cvq is a great idea IMO.

> -       /* Spin for a response, the kick causes an ioport write, trapping
> -        * into the hypervisor, so the request should be handled immediately.
> -        */
> -       while (!virtqueue_get_buf(vi->cvq, &tmp) &&
> -              !virtqueue_is_broken(vi->cvq))
> -               cpu_relax();
> +       virtqueue_wait_for_used(vi->cvq, &tmp);

Do you think that we should continue like nothing happened in case of a timeout?
Shouldn't we reset the device?
What happens if a device completes the control command after timeout?

Thanks

Alvaro