From: Kehuan Feng <kehuan.feng@gmail.com>
To: Cong Wang <xiyou.wangcong@gmail.com>
Cc: Yunsheng Lin <linyunsheng@huawei.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: Fri, 18 Sep 2020 10:06:56 +0800 [thread overview]
Message-ID: <CACS=qqJu6soSDPo+mJhDQwv2Tn-TxjF56w7H8q6zCE=4TJps2g@mail.gmail.com> (raw)
In-Reply-To: <CAM_iQpXiNaushoWjma44X_agPosg9AKk4RzFTX93MSVTM6z3Uw@mail.gmail.com>
Sorry, guys, the experiment environment is no longer existing now. We
finally use fq_codel for online product.
Cong Wang <xiyou.wangcong@gmail.com> 于2020年9月18日周五 上午3:52写道:
>
> 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.
prev parent reply other threads:[~2020-09-18 2:55 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
2020-09-18 2:06 ` Kehuan Feng [this message]
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