From: Fengkehuan Feng <kehuan.feng@gmail.com>
To: Hillf Danton <hdanton@sina.com>
Cc: Jike Song <albcamus@gmail.com>, Josh Hunt <johunt@akamai.com>,
Paolo Abeni <pabeni@redhat.com>,
Jonas Bonn <jonas.bonn@netrounds.com>,
Cong Wang <xiyou.wangcong@gmail.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: Tue, 25 Aug 2020 10:18:05 +0800 [thread overview]
Message-ID: <CACS=qqKhsu6waaXndO5tQL_gC9TztuUQpqQigJA2Ac0y12czMQ@mail.gmail.com> (raw)
In-Reply-To: <20200822032800.16296-1-hdanton@sina.com>
[-- Attachment #1: Type: text/plain, Size: 5412 bytes --]
Hillf,
With the latest version (attached what I have changed on my tree), the
system failed to start up with cpu stalled.
Hillf Danton <hdanton@sina.com> 于2020年8月22日周六 上午11:30写道:
>
>
> On Thu, 20 Aug 2020 20:43:17 +0800 Hillf Danton wrote:
> > Hi Jike,
> >
> > On Thu, 20 Aug 2020 15:43:17 +0800 Jike Song wrote:
> > > Hi Josh,
> > >
> > > On Fri, Jul 3, 2020 at 2:14 AM Josh Hunt <johunt@akamai.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
> >
> > Below is what was sent in reply to this thread early last month with
> > minor tuning, based on the seqlock. Feel free to drop an echo if it
> > makes ant-antenna-size sense in your tests.
> >
> > > 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
> >
> >
> > --- a/include/net/sch_generic.h
> > +++ b/include/net/sch_generic.h
> > @@ -79,6 +79,7 @@ struct Qdisc {
> > #define TCQ_F_INVISIBLE 0x80 /* invisible by default in dump */
> > #define TCQ_F_NOLOCK 0x100 /* qdisc does not require locking */
> > #define TCQ_F_OFFLOADED 0x200 /* qdisc is offloaded to HW */
> > + int pkt_seq;
> > u32 limit;
> > const struct Qdisc_ops *ops;
> > struct qdisc_size_table __rcu *stab;
> > @@ -156,6 +157,7 @@ static inline bool qdisc_is_empty(const
> > static inline bool qdisc_run_begin(struct Qdisc *qdisc)
> > {
> > if (qdisc->flags & TCQ_F_NOLOCK) {
> > + qdisc->pkt_seq++;
> > if (!spin_trylock(&qdisc->seqlock))
> > return false;
> > WRITE_ONCE(qdisc->empty, false);
> > --- a/include/net/pkt_sched.h
> > +++ b/include/net/pkt_sched.h
> > @@ -117,7 +117,9 @@ void __qdisc_run(struct Qdisc *q);
> >
> > static inline void qdisc_run(struct Qdisc *q)
> > {
> > - if (qdisc_run_begin(q)) {
> > + while (qdisc_run_begin(q)) {
> > + int seq = q->pkt_seq;
> > +
> > /* NOLOCK qdisc must check 'state' under the qdisc seqlock
> > * to avoid racing with dev_qdisc_reset()
> > */
> > @@ -125,6 +127,9 @@ static inline void qdisc_run(struct Qdis
> > likely(!test_bit(__QDISC_STATE_DEACTIVATED, &q->state)))
> > __qdisc_run(q);
> > qdisc_run_end(q);
> > +
> > + if (!(q->flags & TCQ_F_NOLOCK) || seq == q->pkt_seq)
> > + return;
> > }
> > }
>
> The echo from Feng indicates that it's hard to conclude that TCQ_F_NOLOCK
> is the culprit, lets try again with it ignored for now.
>
> Every pkt enqueued on pfifo_fast is tracked in the below diff, and those
> pkts enqueued while we're running qdisc are detected and handled to cut
> the chance for the stuck pkts reported.
>
> --- a/include/net/sch_generic.h
> +++ b/include/net/sch_generic.h
> @@ -79,6 +79,7 @@ struct Qdisc {
> #define TCQ_F_INVISIBLE 0x80 /* invisible by default in dump */
> #define TCQ_F_NOLOCK 0x100 /* qdisc does not require locking */
> #define TCQ_F_OFFLOADED 0x200 /* qdisc is offloaded to HW */
> + int pkt_seq;
> u32 limit;
> const struct Qdisc_ops *ops;
> struct qdisc_size_table __rcu *stab;
> --- a/net/sched/sch_generic.c
> +++ b/net/sched/sch_generic.c
> @@ -631,6 +631,7 @@ static int pfifo_fast_enqueue(struct sk_
> return qdisc_drop(skb, qdisc, to_free);
> }
>
> + qdisc->pkt_seq++;
> qdisc_update_stats_at_enqueue(qdisc, pkt_len);
> return NET_XMIT_SUCCESS;
> }
> --- a/include/net/pkt_sched.h
> +++ b/include/net/pkt_sched.h
> @@ -117,7 +117,8 @@ void __qdisc_run(struct Qdisc *q);
>
> static inline void qdisc_run(struct Qdisc *q)
> {
> - if (qdisc_run_begin(q)) {
> + while (qdisc_run_begin(q)) {
> + int seq = q->pkt_seq;
> /* NOLOCK qdisc must check 'state' under the qdisc seqlock
> * to avoid racing with dev_qdisc_reset()
> */
> @@ -125,6 +126,12 @@ static inline void qdisc_run(struct Qdis
> likely(!test_bit(__QDISC_STATE_DEACTIVATED, &q->state)))
> __qdisc_run(q);
> qdisc_run_end(q);
> +
> + /* go another round if there are pkts enqueued after
> + * taking seq_lock
> + */
> + if (seq != q->pkt_seq)
> + continue;
> }
> }
>
>
[-- Attachment #2: fix_nolock_from_hillf.patch --]
[-- Type: application/octet-stream, Size: 1260 bytes --]
--- include/net/sch_generic.h.orig 2020-08-21 15:13:51.787952710 +0800
+++ include/net/sch_generic.h 2020-08-24 22:01:46.718709912 +0800
@@ -79,6 +79,7 @@
#define TCQ_F_INVISIBLE 0x80 /* invisible by default in dump */
#define TCQ_F_NOLOCK 0x100 /* qdisc does not require locking */
#define TCQ_F_OFFLOADED 0x200 /* qdisc is offloaded to HW */
+ int pkt_seq;
u32 limit;
const struct Qdisc_ops *ops;
struct qdisc_size_table __rcu *stab;
--- net/sched/sch_generic.c.orig 2020-08-24 22:02:04.589830751 +0800
+++ net/sched/sch_generic.c 2020-08-24 22:03:48.010728381 +0800
@@ -638,6 +638,8 @@
* so we better not use qdisc_qstats_cpu_backlog_inc()
*/
this_cpu_add(qdisc->cpu_qstats->backlog, pkt_len);
+
+ qdisc->pkt_seq++;
return NET_XMIT_SUCCESS;
}
--- include/net/pkt_sched.h.orig 2020-08-21 15:13:51.787952710 +0800
+++ include/net/pkt_sched.h 2020-08-24 22:06:58.856005213 +0800
@@ -116,9 +116,16 @@
static inline void qdisc_run(struct Qdisc *q)
{
- if (qdisc_run_begin(q)) {
+ while (qdisc_run_begin(q)) {
+ int seq = q->pkt_seq;
__qdisc_run(q);
qdisc_run_end(q);
+
+ /* go another round if there are pkts enqueued after
+ * taking seq_lock
+ */
+ if (seq != q->pkt_seq)
+ continue;
}
}
next prev parent reply other threads:[~2020-08-25 2:18 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 [this message]
[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
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