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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS 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 483BDC432BE for ; Tue, 24 Aug 2021 18:04:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 24021610D0 for ; Tue, 24 Aug 2021 18:04:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239917AbhHXSFA (ORCPT ); Tue, 24 Aug 2021 14:05:00 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43000 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238609AbhHXSEz (ORCPT ); Tue, 24 Aug 2021 14:04:55 -0400 Received: from mail-lj1-x22d.google.com (mail-lj1-x22d.google.com [IPv6:2a00:1450:4864:20::22d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 64D83C061A28 for ; Tue, 24 Aug 2021 11:01:42 -0700 (PDT) Received: by mail-lj1-x22d.google.com with SMTP id j12so24684065ljg.10 for ; Tue, 24 Aug 2021 11:01:42 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=YCxb+VTz4cjVjB3faY8PYmPDiDFElSaMqsPr/FfkL6c=; b=TTbBK+uOHncqHzTPlHlqLNwRCow/uI7O1xrUhx5q6yORLlE6bHsr+dhSaSuXcvPC8W sSo9+Ef3wIF2fxdpq/IxupzammVvj/ottvH7stUJfbMNmbqddK9z1dT8S9X+kA7WeC7B pddO/dstyV3iOaE17BwK+pzEa2wK9BhJlKORo= 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=YCxb+VTz4cjVjB3faY8PYmPDiDFElSaMqsPr/FfkL6c=; b=ahBBuCfTuPkVXCLtI0jEs1bLZgcZEMQRTEKxiwvGzZjs2/5R/P2QOsM/cIy4WWZHqm B7QcOUlZ6fYxZTOknKGBC6NclUs3yBAYFvHR2ZtSiwvFhML9Hm9mjTgPBgUw2a6r2CKX P9iczz3STGLsAw13MfY4fdEr7btXdcn247cu7cObzkOESjdpK5boBEsyp24u6yu8magi EhYAJFkbUi/k/BR4o8NwmTAmYCZFUlE/rJ5x9p3blMABCV699Tn9kCBLVYD4nFYC8Xdu xuSFtyJ7W5W6LHCPySKaBUQTZe6EVAnmLjHdPhfJqS8KwzY23Ha8aMfZBpTD38eWRDvC 2GXQ== X-Gm-Message-State: AOAM531kyzxYZUbT+6T+boOf2cqvYBl+ffBfK+ZYHkHryMGtwI/N8zmw cvAE25ewcdWXwaLJr/8zFHQRPK0eck2HweQD X-Google-Smtp-Source: ABdhPJykaoC93ajXXF6yJu0DxSgV8cmzVAq44qHo4gWErAH/XrP7m0sVaOUwKKcHa/wIzTMVwtCXeA== X-Received: by 2002:a05:651c:1b3:: with SMTP id c19mr32732339ljn.16.1629828099937; Tue, 24 Aug 2021 11:01:39 -0700 (PDT) Received: from mail-lf1-f41.google.com (mail-lf1-f41.google.com. [209.85.167.41]) by smtp.gmail.com with ESMTPSA id p7sm1810316lfa.258.2021.08.24.11.01.38 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 24 Aug 2021 11:01:38 -0700 (PDT) Received: by mail-lf1-f41.google.com with SMTP id o10so47266520lfr.11 for ; Tue, 24 Aug 2021 11:01:38 -0700 (PDT) X-Received: by 2002:a19:500e:: with SMTP id e14mr28777692lfb.487.1629828098025; Tue, 24 Aug 2021 11:01:38 -0700 (PDT) MIME-Version: 1.0 References: <20210824165607.709387-1-sashal@kernel.org> <20210824165607.709387-74-sashal@kernel.org> In-Reply-To: From: Linus Torvalds Date: Tue, 24 Aug 2021 11:01:22 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH 5.13 073/127] pipe: avoid unnecessary EPOLLET wakeups under normal loads To: Sasha Levin Cc: Linux Kernel Mailing List , stable , kernel test robot , Sandeep Patil , Mel Gorman Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Aug 24, 2021 at 10:35 AM Sasha Levin wrote: > > On Tue, Aug 24, 2021 at 10:00:33AM -0700, Linus Torvalds wrote: > > > >Honestly, I don't understand the performance regression, but that's > >likely on me, not on the kernel test robot. > > I'll drop it for now. > > Ideally we wouldn't take it at all, but I don't think any of us wants to > field "my tests have regressed!" questions for the next 5 years or so. I have a theory about what is going on, and it's not a new problem, but it would explain how that test might be so bimodal in performance if you happen to hit the exact right timing. And the test robot just might not have hit the right timing previously. See https://lore.kernel.org/lkml/CAHk-=wiKAg5QtrQOtvKNwkRUn0b2xufO54GPhUoTWxBgDzXWNA@mail.gmail.com/ with a test-patch in the next message in that thread. So it looks like another case of an odd test, but it should be easy enough to make that test happy too. Knock wood. Linus