linux-kernel - Re: [PATCH net-next] sfc: reduce the number of requested xdp ev queues

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Date:   Wed, 16 Dec 2020 23:12:12 +0000
From:   Edward Cree <ecree.xilinx@...il.com>
To:     Jesper Dangaard Brouer <brouer@...hat.com>
Cc:     Ivan Babrou <ivan@...udflare.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
        kernel-team@...udflare.com,
        Martin Habets <habetsm.xilinx@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Marek Majtyka <marekx.majtyka@...el.com>
Subject: Re: [PATCH net-next] sfc: reduce the number of requested xdp ev
 queues

On 16/12/2020 08:45, Jesper Dangaard Brouer wrote:
> So, what I hear is that this fix is just pampering over the real issue.
Yes, it is, but it's better than nothing in the meantime while we work
 out the complete fix.

> I suggest that you/we detect the situation, and have a code path that
> will take a lock (per 16 packets bulk) and solve the issue.
Imho that would _also_ paper over the issue, because it would mean the
 system degraded to a lower performance mode of operation, while still
 appearing to support XDP_TX.  I think that that in general should not
 happen unless there is a way for the user to determine at runtime
 whether it has/should happen.  Perhaps Marek's new XDP feature flags
 could include a "tx-lockless" flag to indicate this?

-ed