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From: Yunsheng Lin <linyunsheng@huawei.com>
To: Cong Wang <xiyou.wangcong@gmail.com>, Jakub Kicinski <kuba@kernel.org>
Cc: David Miller <davem@davemloft.net>,
	Vladimir Oltean <olteanv@gmail.com>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andriin@fb.com>,
	Eric Dumazet <edumazet@google.com>,
	"Wei Wang" <weiwan@google.com>,
	"Cong Wang ." <cong.wang@bytedance.com>,
	Taehee Yoo <ap420073@gmail.com>,
	Linux Kernel Network Developers <netdev@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>, <linuxarm@openeuler.org>,
	Marc Kleine-Budde <mkl@pengutronix.de>,
	<linux-can@vger.kernel.org>
Subject: Re: [RFC v2] net: sched: implement TCQ_F_CAN_BYPASS for lockless qdisc
Date: Wed, 17 Mar 2021 09:14:34 +0800	[thread overview]
Message-ID: <c91af612-24d3-798e-3df3-8bab35e01a38@huawei.com> (raw)
In-Reply-To: <CAM_iQpXvVZxBRHF6PBDOYSOSCj08nPyfcY0adKuuTg=cqffV+w@mail.gmail.com>

On 2021/3/17 6:48, Cong Wang wrote:
> On Mon, Mar 15, 2021 at 2:07 PM Jakub Kicinski <kuba@kernel.org> wrote:
>>
>> I thought pfifo was supposed to be "lockless" and this change
>> re-introduces a lock between producer and consumer, no?
> 
> It has never been truly lockless, it uses two spinlocks in the ring buffer
> implementation, and it introduced a q->seqlock recently, with this patch
> now we have priv->lock, 4 locks in total. So our "lockless" qdisc ends
> up having more locks than others. ;) I don't think we are going to a
> right direction...

Yes, we have 4 locks in total, but lockless qdisc only use two locks
in this patch, which are priv->lock and q->seqlock.

The qdisc at least uses two locks, which is qdisc_lock(q) and q->busylock,
which seems to have bigger contention when concurrent accessing to the
same qdisc.

If we want to reduce the total number of lock, we can use qdisc_lock(q)
for lockless qdisc and remove q->seqlock:)

> 
> Thanks.
> 
> .
> 


  reply	other threads:[~2021-03-17  1:15 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-13  2:47 [PATCH RFC] net: sched: implement TCQ_F_CAN_BYPASS for lockless qdisc Yunsheng Lin
2021-03-14  0:03 ` Vladimir Oltean
2021-03-14 10:15   ` Marc Kleine-Budde
2021-03-15  0:50     ` Yunsheng Lin
2021-03-15  3:10 ` [RFC v2] " Yunsheng Lin
2021-03-15 12:29   ` Vladimir Oltean
2021-03-15 13:09   ` Marc Kleine-Budde
2021-03-15 18:53   ` Jakub Kicinski
2021-03-16  0:35     ` Yunsheng Lin
2021-03-16  3:47       ` [Linuxarm] " Yunsheng Lin
2021-03-16  8:15       ` Eric Dumazet
2021-03-16 12:36         ` Yunsheng Lin
2021-03-16 22:48     ` Cong Wang
2021-03-17  1:14       ` Yunsheng Lin [this message]
2021-03-17 13:35       ` Toke Høiland-Jørgensen
2021-03-17 13:45         ` Jason A. Donenfeld
2021-03-18  7:33           ` [Linuxarm] " Yunsheng Lin
2021-03-19 18:15             ` Cong Wang
2021-03-22  0:55               ` Yunsheng Lin
2021-03-24  1:49                 ` Cong Wang
2021-03-24  2:36                   ` Yunsheng Lin
2021-03-19 19:03             ` Jason A. Donenfeld
2021-03-22  1:05               ` Yunsheng Lin
2021-03-18  7:10   ` Ahmad Fatoum
2021-03-18  7:46     ` Yunsheng Lin
2021-03-18  9:09       ` Ahmad Fatoum

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