From: Kehuan Feng <kehuan.feng@gmail.com>
To: Hillf Danton <hdanton@sina.com>
Cc: Paolo Abeni <pabeni@redhat.com>,
Cong Wang <xiyou.wangcong@gmail.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>
Subject: Re: Packet gets stuck in NOLOCK pfifo_fast qdisc
Date: Fri, 4 Sep 2020 11:20:57 +0800 [thread overview]
Message-ID: <CACS=qqLKSpnRrgROm8jzzFid3MH97phPXWsk28b371dfu0mnVA@mail.gmail.com> (raw)
In-Reply-To: <20200903101957.428-1-hdanton@sina.com>
Hi Hillf, Cong, Paolo,
Sorry for the late reply due to other urgent task.
I tried Hillf's patch (shown below on my tree) and it doesn't help and
the jitter shows up very quickly.
--- ./include/net/sch_generic.h.orig 2020-08-21 15:13:51.787952710 +0800
+++ ./include/net/sch_generic.h 2020-09-04 10:48:32.081217156 +0800
@@ -108,6 +108,7 @@
spinlock_t busylock ____cacheline_aligned_in_smp;
spinlock_t seqlock;
+ int run, seq;
};
static inline void qdisc_refcount_inc(struct Qdisc *qdisc)
@@ -127,8 +128,11 @@
static inline bool qdisc_run_begin(struct Qdisc *qdisc)
{
if (qdisc->flags & TCQ_F_NOLOCK) {
+ qdisc->run++;
+ smp_wmb();
if (!spin_trylock(&qdisc->seqlock))
return false;
+ qdisc->seq = qdisc->run;
} else if (qdisc_is_running(qdisc)) {
return false;
}
@@ -143,8 +147,15 @@
static inline void qdisc_run_end(struct Qdisc *qdisc)
{
write_seqcount_end(&qdisc->running);
- if (qdisc->flags & TCQ_F_NOLOCK)
+ if (qdisc->flags & TCQ_F_NOLOCK) {
+ int seq = qdisc->seq;
+
spin_unlock(&qdisc->seqlock);
+ smp_rmb();
+ if (seq != qdisc->run)
+ __netif_schedule(qdisc);
+
+ }
}
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).
--- ./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.
Anyway, we are going to use fq_codel instead, since CentOS 8/kernel
4.18 also uses fq_codel as the default qdisc, not sure whehter they
found some thing related to this.
Thanks,
Kehuan
Hillf Danton <hdanton@sina.com> 于2020年9月3日周四 下午6:20写道:
>
>
> On Thu, 03 Sep 2020 10:39:54 +0200 Paolo Abeni wrote:
> > On Wed, 2020-09-02 at 22:01 -0700, Cong Wang wrote:
> > > Can you test the attached one-line fix? I think we are overthinking,
> > > probably all
> > > we need here is a busy wait.
> >
> > I think that will solve, but I also think that will kill NOLOCK
> > performances due to really increased contention.
> >
> > At this point I fear we could consider reverting the NOLOCK stuff.
> > I personally would hate doing so, but it looks like NOLOCK benefits are
> > outweighed by its issues.
> >
> > Any other opinion more than welcome!
>
> Hi Paolo,
>
> I suspect it's too late to fix the -27% below.
> Surgery to cut NOLOCK seems too early before the fix.
>
> Hillf
>
> >pktgen threads vanilla patched[II] delta
> >nr kpps kpps %
> >1 3240 3240 0
> >2 3910 2830 -27%
> >4 5140 5140 0
>
next prev parent reply other threads:[~2020-09-04 3:21 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 [this message]
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
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