From: Yunsheng Lin <linyunsheng@huawei.com>
To: Cong Wang <xiyou.wangcong@gmail.com>,
Kehuan Feng <kehuan.feng@gmail.com>
Cc: 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: Mon, 14 Sep 2020 10:10:31 +0800 [thread overview]
Message-ID: <c97908eb-5a0b-363c-93fd-59c037bbd9f0@huawei.com> (raw)
In-Reply-To: <CAM_iQpUq9-wja3JHz9+TMeXGyAOmJfZDxWUZJ9v25i7vd0Z-Wg@mail.gmail.com>
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).
Kehuan, do you care to try the below patch if it is the same problem?
diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
index d60e7c3..c97c1ed 100644
--- a/include/net/sch_generic.h
+++ b/include/net/sch_generic.h
@@ -36,6 +36,7 @@ struct qdisc_rate_table {
enum qdisc_state_t {
__QDISC_STATE_SCHED,
__QDISC_STATE_DEACTIVATED,
+ __QDISC_STATE_ENQUEUED,
};
struct qdisc_size_table {
diff --git a/net/core/dev.c b/net/core/dev.c
index 0362419..5985648 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3748,6 +3748,8 @@ static inline int __dev_xmit_skb(struct sk_buff *skb, struct Qdisc *q,
qdisc_calculate_pkt_len(skb, q);
if (q->flags & TCQ_F_NOLOCK) {
+ set_bit(__QDISC_STATE_ENQUEUED, &q->state);
+ smp_mb__after_atomic();
rc = q->enqueue(skb, q, &to_free) & NET_XMIT_MASK;
qdisc_run(q);
diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 265a61d..c389641 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -381,6 +381,8 @@ void __qdisc_run(struct Qdisc *q)
int quota = dev_tx_weight;
int packets;
+ clear_bit(__QDISC_STATE_ENQUEUED, &q->state);
+ smp_mb__after_atomic();
while (qdisc_restart(q, &packets)) {
quota -= packets;
if (quota <= 0) {
@@ -388,6 +390,9 @@ void __qdisc_run(struct Qdisc *q)
break;
}
}
+
+ if (test_bit(__QDISC_STATE_ENQUEUED, &q->state))
+ __netif_schedule(q);
}
unsigned long dev_trans_start(struct net_device *dev)
>
> Thanks.
>
next prev parent reply other threads:[~2020-09-14 2:10 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 [this message]
2020-09-17 19:52 ` Cong Wang
2020-09-18 2:06 ` Kehuan Feng
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