netdev - Re: Packet gets stuck in NOLOCK pfifo

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Date:   Thu, 20 Aug 2020 15:43:17 +0800
From:   Jike Song <albcamus@...il.com>
To:     Josh Hunt <johunt@...mai.com>
Cc:     Paolo Abeni <pabeni@...hat.com>,
        Jonas Bonn <jonas.bonn@...rounds.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Michael Zhivich <mzhivich@...mai.com>,
        David Miller <davem@...emloft.net>,
        John Fastabend <john.fastabend@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        kehuan.feng@...il.com
Subject: Re: Packet gets stuck in NOLOCK pfifo_fast qdisc

Hi Josh,

On Fri, Jul 3, 2020 at 2:14 AM Josh Hunt <johunt@...mai.com> wrote:
{snip}
> Initial results with Cong's patch look promising, so far no stalls. We
> will let it run over the long weekend and report back on Tuesday.
>
> Paolo - I have concerns about possible performance regression with the
> change as well. If you can gather some data that would be great. If
> things look good with our low throughput test over the weekend we can
> also try assessing performance next week.
>

We met possibly the same problem when testing nvidia/mellanox's
GPUDirect RDMA product, we found that changing NET_SCH_DEFAULT to
DEFAULT_FQ_CODEL mitigated the problem, having no idea why. Maybe you
can also have a try?

Besides, our testing is pretty complex, do you have a quick test to
reproduce it?

-- 
Thanks,
Jike