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

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Date:   Tue, 12 Apr 2022 14:49:06 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Ray Jui <ray.jui@...adcom.com>
Cc:     Michael Chan <michael.chan@...adcom.com>,
        "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, 12 Apr 2022 12:34:23 -0700 Ray Jui wrote:
> Sure, that is the general error recovery case which is very different
> from this specific recovery case we are discussing here. This specific
> recovery is solely performed by driver (without resetting firmware and
> chip) on a per NAPI ring set basis. While a specific NAPI ring set is
> being recovered, traffic is still going with the rest of the NAPI ring
> sets. Average recovery time is in the 1 - 2 ms range in this type of
> recovery.
> 
> Also as I already said, 'netif_carrier_off' is not an option given that
> the RoCE/infiniband subsystem has a dependency on 'netif_carrier_status'
> for many of their operations.
> 
> Basically I'm looking for a solution that allows one to be able to:
> 1) quieice traffic and perform recovery on a per NAPI ring set basis
> 2) During recovery, it does not cause any drastic effect on RoCE
> 
> 'txq_trans_update' may not be the most optimal solution, but it is a
> solution that satisfies the two requirements above. If there are any
> other option that is considered more optimal than 'txq_trans_update' and
> can satisfy the two requirements, please let me know.

The optimal solution would be to not have to reset your rings and
pretend like nothing happened :/ If you can't reset the ring in time
you'll have to live with the splat. End of story.