netdev - Re: [RFC] Applicability of using 'txq_trans

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Date:   Tue, 12 Apr 2022 12:19:04 -0700
From:   Michael Chan <michael.chan@...adcom.com>
To:     Ray Jui <ray.jui@...adcom.com>
Cc:     Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Netdev <netdev@...r.kernel.org>
Subject: Re: [RFC] Applicability of using 'txq_trans_update' during ring recovery

On Tue, Apr 12, 2022 at 11:36 AM Ray Jui <ray.jui@...adcom.com> wrote:
> On 4/12/22 11:24, Michael Chan wrote:
> > On Tue, Apr 12, 2022 at 11:08 AM Ray Jui <ray.jui@...adcom.com> wrote:
> >
> >> Can you please also comment on whether 'txq_trans_update' is considered
> >> an acceptable approach in this particular scenario?
> >
> > In my opinion, updating trans_start to the current jiffies to prevent
> > TX timeout is not a good solution.  It just buys you the arbitrary TX
> > timeout period before the next TX timeout.  If you take more than this
> > time to restart the TX queue, you will still get TX timeout.
>
> However, one can argue that the recovery work is expected to be finished
> in much less time than any arbitrary TX timeout period. If the recovery
> of the particular NAPI ring set is taking more than an arbitrary TX
> timeout period, then something is wrong and we should really TX timeout.

Even if it should work in a specific case, you are still expanding the
definition of TX timeout to be no shorter than this specific recovery
time.

Our general error recovery time that includes firmware and chip reset
can take longer than the TX timeout period.  And we call
netif_carrier_off() for the whole duration.

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