From: Yunsheng Lin <linyunsheng@huawei.com>
To: "Jason A. Donenfeld" <Jason@zx2c4.com>,
"Toke Høiland-Jørgensen" <toke@redhat.com>
Cc: Cong Wang <xiyou.wangcong@gmail.com>,
Jakub Kicinski <kuba@kernel.org>,
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: [Linuxarm] Re: [RFC v2] net: sched: implement TCQ_F_CAN_BYPASS for lockless qdisc
Date: Thu, 18 Mar 2021 15:33:04 +0800 [thread overview]
Message-ID: <3bae7b26-9d7f-15b8-d466-ff5c26d08b35@huawei.com> (raw)
In-Reply-To: <CAHmME9qDU7VRmBV+v0tzLiUpMJykjswSDwqc9P43ZwG1UD7mzw@mail.gmail.com>
On 2021/3/17 21:45, Jason A. Donenfeld wrote:
> On 3/17/21, Toke Høiland-Jørgensen <toke@redhat.com> wrote:
>> Cong Wang <xiyou.wangcong@gmail.com> writes:
>>
>>> 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...
>>
>> Just a thought, have you guys considered adopting the lockless MSPC ring
>> buffer recently introduced into Wireguard in commit:
>>
>> 8b5553ace83c ("wireguard: queueing: get rid of per-peer ring buffers")
>>
>> Jason indicated he was willing to work on generalising it into a
>> reusable library if there was a use case for it. I haven't quite though
>> through the details of whether this would be such a use case, but
>> figured I'd at least mention it :)
>
> That offer definitely still stands. Generalization sounds like a lot of fun.
>
> Keep in mind though that it's an eventually consistent queue, not an
> immediately consistent one, so that might not match all use cases. It
> works with wg because we always trigger the reader thread anew when it
> finishes, but that doesn't apply to everyone's queueing setup.
Thanks for mentioning this.
"multi-producer, single-consumer" seems to match the lockless qdisc's
paradigm too, for now concurrent enqueuing/dequeuing to the pfifo_fast's
queues() is not allowed, it is protected by producer_lock or consumer_lock.
So it would be good to has lockless concurrent enqueuing, while dequeuing
can be protected by qdisc_lock() or q->seqlock, which meets the "multi-producer,
single-consumer" paradigm.
But right now lockless qdisc has some packet stuck problem, which I tried to
fix in [1].
If the packet stuck problem for lockless qdisc can be fixed, and we can do
more optimization on lockless qdisc, including the one you mention:)
1.https://patchwork.kernel.org/project/netdevbpf/patch/1616050402-37023-1-git-send-email-linyunsheng@huawei.com/
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next prev parent reply other threads:[~2021-03-18 7:34 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
2021-03-17 13:35 ` Toke Høiland-Jørgensen
2021-03-17 13:45 ` Jason A. Donenfeld
2021-03-18 7:33 ` Yunsheng Lin [this message]
2021-03-19 18:15 ` [Linuxarm] " 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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