From: Cong Wang <xiyou.wangcong@gmail.com>
To: Yunsheng Lin <linyunsheng@huawei.com>
Cc: Kehuan Feng <kehuan.feng@gmail.com>,
Hillf Danton <hdanton@sina.com>, Paolo Abeni <pabeni@redhat.com>,
Jike Song <albcamus@gmail.com>, Josh Hunt <johunt@akamai.com>,
Jonas Bonn <jonas.bonn@netrounds.com>,
Michael Zhivich <mzhivich@akamai.com>,
David Miller <davem@davemloft.net>,
John Fastabend <john.fastabend@gmail.com>,
LKML <linux-kernel@vger.kernel.org>,
Netdev <netdev@vger.kernel.org>,
"linuxarm@huawei.com" <linuxarm@huawei.com>
Subject: Re: Packet gets stuck in NOLOCK pfifo_fast qdisc
Date: Thu, 17 Sep 2020 12:52:32 -0700 [thread overview]
Message-ID: <CAM_iQpXiNaushoWjma44X_agPosg9AKk4RzFTX93MSVTM6z3Uw@mail.gmail.com> (raw)
In-Reply-To: <c97908eb-5a0b-363c-93fd-59c037bbd9f0@huawei.com>
On Sun, Sep 13, 2020 at 7:10 PM Yunsheng Lin <linyunsheng@huawei.com> wrote:
>
> On 2020/9/11 4:19, Cong Wang wrote:
> > On Thu, Sep 3, 2020 at 8:21 PM Kehuan Feng <kehuan.feng@gmail.com> wrote:
> >> I also tried Cong's patch (shown below on my tree) and it could avoid
> >> the issue (stressing for 30 minutus for three times and not jitter
> >> observed).
> >
> > Thanks for verifying it!
> >
> >>
> >> --- ./include/net/sch_generic.h.orig 2020-08-21 15:13:51.787952710 +0800
> >> +++ ./include/net/sch_generic.h 2020-09-03 21:36:11.468383738 +0800
> >> @@ -127,8 +127,7 @@
> >> static inline bool qdisc_run_begin(struct Qdisc *qdisc)
> >> {
> >> if (qdisc->flags & TCQ_F_NOLOCK) {
> >> - if (!spin_trylock(&qdisc->seqlock))
> >> - return false;
> >> + spin_lock(&qdisc->seqlock);
> >> } else if (qdisc_is_running(qdisc)) {
> >> return false;
> >> }
> >>
> >> I am not actually know what you are discussing above. It seems to me
> >> that Cong's patch is similar as disabling lockless feature.
> >
> >>From performance's perspective, yeah. Did you see any performance
> > downgrade with my patch applied? It would be great if you can compare
> > it with removing NOLOCK. And if the performance is as bad as no
> > NOLOCK, then we can remove the NOLOCK bit for pfifo_fast, at least
> > for now.
>
> It seems the lockless qdisc may have below concurrent problem:
> cpu0: cpu1:
> q->enqueue .
> qdisc_run_begin(q) .
> __qdisc_run(q) ->qdisc_restart() -> dequeue_skb() .
> -> sch_direct_xmit() .
> .
> q->enqueue
> qdisc_run_begin(q)
> qdisc_run_end(q)
>
>
> cpu1 enqueue a skb without calling __qdisc_run(), and cpu0 did not see the
> enqueued skb when calling __qdisc_run(q) because cpu1 may enqueue the skb
> after cpu0 called __qdisc_run(q) and before cpu0 called qdisc_run_end(q).
This is the same problem that my patch fixes, I do not know
why you are suggesting another patch despite quoting mine.
Please read the whole thread if you want to participate.
Thanks.
next prev parent reply other threads:[~2020-09-17 19:58 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-09 6:46 Packet gets stuck in NOLOCK pfifo_fast qdisc Jonas Bonn
2019-10-09 19:14 ` Paolo Abeni
2019-10-10 6:27 ` Jonas Bonn
2019-10-11 0:39 ` Jonas Bonn
2020-06-23 13:42 ` Michael Zhivich
2020-06-30 19:14 ` Josh Hunt
2020-07-01 7:53 ` Jonas Bonn
2020-07-01 16:05 ` Cong Wang
2020-07-01 19:58 ` Cong Wang
2020-07-01 22:02 ` Josh Hunt
2020-07-02 6:14 ` Jonas Bonn
2020-07-02 9:45 ` Paolo Abeni
2020-07-02 18:08 ` Josh Hunt
2020-07-07 14:18 ` Paolo Abeni
2020-07-08 20:16 ` Cong Wang
2020-07-09 9:20 ` Paolo Abeni
2020-07-08 20:33 ` Zhivich, Michael
2020-08-20 7:43 ` Jike Song
2020-08-20 18:13 ` Josh Hunt
[not found] ` <20200822032800.16296-1-hdanton@sina.com>
2020-08-25 2:18 ` Fengkehuan Feng
[not found] ` <20200825032312.11776-1-hdanton@sina.com>
2020-08-25 7:14 ` Fengkehuan Feng
[not found] ` <20200825162329.11292-1-hdanton@sina.com>
2020-08-26 2:38 ` Kehuan Feng
[not found] ` <CACS=qqKptAQQGiMoCs1Zgs9S4ZppHhasy1AK4df2NxnCDR+vCw@mail.gmail.com>
[not found] ` <5f46032e.1c69fb81.9880c.7a6cSMTPIN_ADDED_MISSING@mx.google.com>
2020-08-27 6:56 ` Kehuan Feng
[not found] ` <20200827125747.5816-1-hdanton@sina.com>
2020-08-28 1:45 ` Kehuan Feng
2020-09-03 5:01 ` Cong Wang
2020-09-03 8:39 ` Paolo Abeni
2020-09-03 17:43 ` Cong Wang
2020-09-04 5:07 ` John Fastabend
2020-09-10 20:15 ` Cong Wang
2020-09-10 21:07 ` John Fastabend
2020-09-10 21:40 ` Paolo Abeni
2021-04-02 19:25 ` Jiri Kosina
2021-04-02 19:33 ` Josh Hunt
[not found] ` <20210403003537.2032-1-hdanton@sina.com>
2021-04-03 12:23 ` Jiri Kosina
2021-04-06 0:55 ` Yunsheng Lin
2021-04-06 7:06 ` Michal Kubecek
2021-04-06 10:13 ` Juergen Gross
2021-04-06 12:17 ` Yunsheng Lin
2021-04-06 1:49 ` Cong Wang
2021-04-06 2:46 ` Yunsheng Lin
2021-04-06 7:31 ` Michal Kubecek
2021-04-06 12:24 ` Yunsheng Lin
[not found] ` <20200903101957.428-1-hdanton@sina.com>
2020-09-04 3:20 ` Kehuan Feng
2020-09-10 20:19 ` Cong Wang
2020-09-14 2:10 ` Yunsheng Lin
2020-09-17 19:52 ` Cong Wang [this message]
2020-09-18 2:06 ` Kehuan Feng
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