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From: Marc Kleine-Budde <mkl@pengutronix.de>
To: Vladimir Oltean <olteanv@gmail.com>,
	Yunsheng Lin <linyunsheng@huawei.com>
Cc: davem@davemloft.net, kuba@kernel.org, ast@kernel.org,
	daniel@iogearbox.net, andriin@fb.com, edumazet@google.com,
	weiwan@google.com, cong.wang@bytedance.com, ap420073@gmail.com,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
	linuxarm@openeuler.org, pabeni@redhat.com,
	linux-can <linux-can@vger.kernel.org>
Subject: Re: [PATCH RFC] net: sched: implement TCQ_F_CAN_BYPASS for lockless qdisc
Date: Sun, 14 Mar 2021 11:15:07 +0100	[thread overview]
Message-ID: <298228b3-af1d-6907-92a3-b273dad7a150@pengutronix.de> (raw)
In-Reply-To: <20210314000350.2mrhvprsi77qwqdi@skbuf>


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Cc += linux-can@vger.kernel.org

On 3/14/21 1:03 AM, Vladimir Oltean wrote:
> On Sat, Mar 13, 2021 at 10:47:47AM +0800, Yunsheng Lin wrote:
>> Currently pfifo_fast has both TCQ_F_CAN_BYPASS and TCQ_F_NOLOCK
>> flag set, but queue discipline by-pass does not work for lockless
>> qdisc because skb is always enqueued to qdisc even when the qdisc
>> is empty, see __dev_xmit_skb().
>>
>> This patch calles sch_direct_xmit() to transmit the skb directly
>> to the driver for empty lockless qdisc too, which aviod enqueuing
>> and dequeuing operation. qdisc->empty is set to false whenever a
>> skb is enqueued, and is set to true when skb dequeuing return NULL,
>> see pfifo_fast_dequeue().
>>
>> Also, qdisc is scheduled at the end of qdisc_run_end() when q->empty
>> is false to avoid packet stuck problem.
>>
>> The performance for ip_forward test increases about 10% with this
>> patch.
>>
>> Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
>> ---
> 
> I can confirm the ~10% IP forwarding throughput improvement brought by
> this patch, but as you might be aware, there was a previous attempt to
> add qdisc bypass to pfifo_fast by Paolo Abeni:
> https://lore.kernel.org/netdev/661cc33a-5f65-2769-cc1a-65791cb4b131@pengutronix.de/
> It was reverted because TX reordering was observed with SocketCAN
> (although, presumably it should also be seen with Ethernet and such).

Thanks for testing that, I just stumbled over this patch by accident.

Marc

-- 
Pengutronix e.K.                 | Marc Kleine-Budde           |
Embedded Linux                   | https://www.pengutronix.de  |
Vertretung West/Dortmund         | Phone: +49-231-2826-924     |
Amtsgericht Hildesheim, HRA 2686 | Fax:   +49-5121-206917-5555 |


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  reply	other threads:[~2021-03-14 10:16 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 [this message]
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           ` [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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