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=-2.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 9F54FC433E0 for ; Tue, 16 Mar 2021 18:42:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 747C26510F for ; Tue, 16 Mar 2021 18:42:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240070AbhCPSmE (ORCPT ); Tue, 16 Mar 2021 14:42:04 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50246 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231668AbhCPSlk (ORCPT ); Tue, 16 Mar 2021 14:41:40 -0400 Received: from mail-pf1-x42c.google.com (mail-pf1-x42c.google.com [IPv6:2607:f8b0:4864:20::42c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C35B5C06174A; Tue, 16 Mar 2021 11:41:39 -0700 (PDT) Received: by mail-pf1-x42c.google.com with SMTP id 18so9429103pfo.6; Tue, 16 Mar 2021 11:41:39 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=1LsuKaONtTkRfqGPcyI045IeBZRuFxo9057hwlVxGB8=; b=c5tx2uRwSqjf4JqGSueVbn8FxluuV5CsctUBo+txrZJm3mUNKfJm6eseAjI+hWK6HD Jb6BpT24VMuR/nwtPq6eYA9sX8HBsFsxcfB/XWH/oIHBCjspSOZU9/pnFeuZ+pxWwJqN xy8jTDRXCGawyo6AepmAK2o5mdhXYTbfEtxKdCJ4AV+oCoTrO/I8iK6ZCJwSFr4yUgsk 1RnYJ5m0Cct/1uQkjnj+I71FoUqKXlwZdDQ9XBQsXlPN+AL0ikUPJi03V/QYX6l0lB/P fO6MVV9fpE9qlDNyT4q0x/TPENRRUf1Z9kWZ6qBUIQAKHL3JodSI4pe9uRFU+RZwDuqy gzYg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=1LsuKaONtTkRfqGPcyI045IeBZRuFxo9057hwlVxGB8=; b=tabjHpIwNUrmbYULzSeWz7tue/8Vzwes61K8V0Ab3ECnCpvAO4TNUidmXgwFGCt6kO wiDANbvdDIWxyJgUVc0PiwUbESIdUH/iozJ+AJ5oq65LnwYvg1mdJ18gZf1RZ7wuLN9S CxI4duAnw+g+bB4ZbxByTEg++fZuv+LLSy8aIcRPRwQA1PchWiNkPk040dBzeZkcKOcg ykZ3Z9scHBZN/Hw7X7QzbSsIN2xn5jqjl1PgdUz8mM2Z6ogyc1DZx1Yq1ZUSVzm2DGTb +ss56mIzzvapiTKyOA4gfETt7aJWq+7vAQn6aVhPnmcYZ+5TSQn0WehowTOnrcQb59Sv 140g== X-Gm-Message-State: AOAM531ss8IaAGzySE3XuobWa1f4TD3ILd0DPzzX+ZlwP29CPzgrASfn fC2hqsuvijkFGZI5Henl+QNONyCryceGvAvc0Cs= X-Google-Smtp-Source: ABdhPJz1QLJiX0jVTh0D2aZJZHxm4rxojewAyFQRvPT/TQfn2DZYKWihd29lqOlLA325oH2vtfBGMThaYygRKZ6WtjM= X-Received: by 2002:a63:1266:: with SMTP id 38mr909777pgs.266.1615920099302; Tue, 16 Mar 2021 11:41:39 -0700 (PDT) MIME-Version: 1.0 References: <1615800610-34700-1-git-send-email-linyunsheng@huawei.com> In-Reply-To: <1615800610-34700-1-git-send-email-linyunsheng@huawei.com> From: Cong Wang Date: Tue, 16 Mar 2021 11:41:28 -0700 Message-ID: Subject: Re: [PATCH net-next] net: sched: remove unnecessay lock protection for skb_bad_txq/gso_skb To: Yunsheng Lin Cc: David Miller , Jakub Kicinski , Jamal Hadi Salim , Jiri Pirko , Linux Kernel Network Developers , LKML , linuxarm@openeuler.org Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Mar 15, 2021 at 2:29 AM Yunsheng Lin wrote: > > Currently qdisc_lock(q) is taken before enqueuing and dequeuing > for lockless qdisc's skb_bad_txq/gso_skb queue, qdisc->seqlock is > also taken, which can provide the same protection as qdisc_lock(q). > > This patch removes the unnecessay qdisc_lock(q) protection for > lockless qdisc' skb_bad_txq/gso_skb queue. > > And dev_reset_queue() takes the qdisc->seqlock for lockless qdisc > besides taking the qdisc_lock(q) when doing the qdisc reset, > some_qdisc_is_busy() takes both qdisc->seqlock and qdisc_lock(q) > when checking qdisc status. It is unnecessary to take both lock > while the fast path only take one lock, so this patch also changes > it to only take qdisc_lock(q) for locked qdisc, and only take > qdisc->seqlock for lockless qdisc. > > Since qdisc->seqlock is taken for lockless qdisc when calling > qdisc_is_running() in some_qdisc_is_busy(), use qdisc->running > to decide if the lockless qdisc is running. What's the benefit here? Since qdisc->q.lock is also per-qdisc, so there is no actual contention to take it when we already acquire q->seqlock, right? Also, is ->seqlock supposed to be used for protecting skb_bad_txq etc.? From my understanding, it was introduced merely for replacing __QDISC_STATE_RUNNING. If you want to extend it, you probably have to rename it too. Thanks.