From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 18E58C433E6 for ; Thu, 18 Mar 2021 07:34:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CA10064F40 for ; Thu, 18 Mar 2021 07:34:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229741AbhCRHeH (ORCPT ); Thu, 18 Mar 2021 03:34:07 -0400 Received: from szxga02-in.huawei.com ([45.249.212.188]:3490 "EHLO szxga02-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229621AbhCRHd0 (ORCPT ); Thu, 18 Mar 2021 03:33:26 -0400 Received: from DGGEMM403-HUB.china.huawei.com (unknown [172.30.72.54]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4F1JcT5N0PzRRH8; Thu, 18 Mar 2021 15:31:37 +0800 (CST) Received: from dggpemm500005.china.huawei.com (7.185.36.74) by DGGEMM403-HUB.china.huawei.com (10.3.20.211) with Microsoft SMTP Server (TLS) id 14.3.498.0; Thu, 18 Mar 2021 15:33:05 +0800 Received: from [127.0.0.1] (10.69.30.204) by dggpemm500005.china.huawei.com (7.185.36.74) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256) id 15.1.2106.2; Thu, 18 Mar 2021 15:33:05 +0800 Subject: Re: [Linuxarm] Re: [RFC v2] net: sched: implement TCQ_F_CAN_BYPASS for lockless qdisc To: "Jason A. Donenfeld" , =?UTF-8?Q?Toke_H=c3=b8iland-J=c3=b8rgensen?= CC: Cong Wang , Jakub Kicinski , David Miller , Vladimir Oltean , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Eric Dumazet , "Wei Wang" , "Cong Wang ." , Taehee Yoo , Linux Kernel Network Developers , LKML , , Marc Kleine-Budde , References: <1615603667-22568-1-git-send-email-linyunsheng@huawei.com> <1615777818-13969-1-git-send-email-linyunsheng@huawei.com> <20210315115332.1647e92b@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> <87eegddhsj.fsf@toke.dk> From: Yunsheng Lin Message-ID: <3bae7b26-9d7f-15b8-d466-ff5c26d08b35@huawei.com> Date: Thu, 18 Mar 2021 15:33:04 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.2.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 8bit X-Originating-IP: [10.69.30.204] X-ClientProxiedBy: dggeme706-chm.china.huawei.com (10.1.199.102) To dggpemm500005.china.huawei.com (7.185.36.74) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021/3/17 21:45, Jason A. Donenfeld wrote: > On 3/17/21, Toke Høiland-Jørgensen wrote: >> Cong Wang writes: >> >>> On Mon, Mar 15, 2021 at 2:07 PM Jakub Kicinski 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/ > _______________________________________________ > Linuxarm mailing list -- linuxarm@openeuler.org > To unsubscribe send an email to linuxarm-leave@openeuler.org >