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=-0.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS autolearn=ham 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 1EFA4C43381 for ; Fri, 22 Mar 2019 15:18:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DCEB821917 for ; Fri, 22 Mar 2019 15:18:06 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="o128i09n" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727146AbfCVPSF (ORCPT ); Fri, 22 Mar 2019 11:18:05 -0400 Received: from mail-wm1-f65.google.com ([209.85.128.65]:36621 "EHLO mail-wm1-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726090AbfCVPSF (ORCPT ); Fri, 22 Mar 2019 11:18:05 -0400 Received: by mail-wm1-f65.google.com with SMTP id h18so2574667wml.1 for ; Fri, 22 Mar 2019 08:18:04 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=8IJfqfnjOJ25XQBIvUTi0RtgRU4/rSyaKxSuiAVt9wg=; b=o128i09nq3xTBbzSP4mMhpkOsMf/wDkevfkSUNdLI+pq8CUEnH/LlUJsFg3YBJ9qXQ G2mU9Q31x1S3MjG21ld8UcVHyB6YI6TwUsGReFsHlUIYP/MlNC7vLMeLLf3wxqaka32t jXLN91/ZaWAxGLLNECAxmaLspwePsRb+S+E93yNyl9L6S8utDbhzxD/G6V14UbmSZ/sR GKnggU/Prne04Bcg7/hfVOZGLvQJN2/c9hjwoALOdh1JxZNXitAmn4vfpBr0bA+Brv3N l1KZRKN8tQ+VRh/XF1n81dxAI7RM2JsV+NQkf8IRYQ4lL8q/eE30wigQfwd6PeYn2G2f Gx4A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=8IJfqfnjOJ25XQBIvUTi0RtgRU4/rSyaKxSuiAVt9wg=; b=geU8M7gNK5awVoBGeaELjLmfFLRkSoyUr46pP6S/36mm318oagc6j95Qbs4xb+ZNqG S6SY589rSTzpstrHdyAi8MZv1tZOOriH6ztFifAxXzl3zg/n2WrhQctm3pkfMVW/H08a 0dGqIUp1c+RirgDM617D4d/WhFbHVOMCc6vam/mr/RJQzJN5B9zQw37OsQKbZyp/xQ26 kwQbPQ/o3F4U++o2N1LSdSMs/4YYPkl5+IYl6aP3O1fV/ZocutCywdpgOSNCUVQWlYEK 1aZJQkMiBnYIQLODdCHKBhYMnrs8Ot2hCtZEjVsQXghiu6RzL6E4BakQ5CxRUaiislla CHXA== X-Gm-Message-State: APjAAAUZ5dxmkjmQAbfQUosuldf9VrH1Je5gbAVR8zk7Aw328aVrAYBN qaSaiqOLZ4cLIh49AC99y78= X-Google-Smtp-Source: APXvYqyneKxShWpjxE4ugxFV2bMiSqlwh0/vzRa7bU7v3FxZWcdD6JHoMnY8+z9i71GBE2XN5zRfEA== X-Received: by 2002:a7b:c446:: with SMTP id l6mr3394535wmi.80.1553267883598; Fri, 22 Mar 2019 08:18:03 -0700 (PDT) Received: from [172.31.96.190] ([195.39.71.253]) by smtp.gmail.com with ESMTPSA id o127sm10503884wmo.20.2019.03.22.08.18.02 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 22 Mar 2019 08:18:02 -0700 (PDT) Subject: Re: [PATCH net-next v3 1/2] net: sched: add empty status flag for NOLOCK qdisc To: Paolo Abeni , netdev@vger.kernel.org Cc: "David S. Miller" , Eric Dumazet , John Fastabend , Ivan Vecera References: <5c30962d8213c8483aee810aa447028e56de963e.1553263445.git.pabeni@redhat.com> From: Eric Dumazet Message-ID: Date: Fri, 22 Mar 2019 08:18:02 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <5c30962d8213c8483aee810aa447028e56de963e.1553263445.git.pabeni@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 03/22/2019 08:01 AM, Paolo Abeni wrote: > The queue is marked not empty after acquiring the seqlock, > and it's up to the NOLOCK qdisc clearing such flag on dequeue. > Since the empty status lays on the same cache-line of the > seqlock, it's always hot on cache during the updates. > > This makes the empty flag update a little bit loosy. Given > the lack of synchronization between enqueue and dequeue, this > is unavoidable. > Reviewed-by: Eric Dumazet