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 517CFC2BB40 for ; Thu, 17 Dec 2020 10:50:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0CB592389A for ; Thu, 17 Dec 2020 10:50:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727767AbgLQKtr (ORCPT ); Thu, 17 Dec 2020 05:49:47 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58730 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727416AbgLQKtr (ORCPT ); Thu, 17 Dec 2020 05:49:47 -0500 Received: from mail-ed1-x533.google.com (mail-ed1-x533.google.com [IPv6:2a00:1450:4864:20::533]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AC29BC0617B0 for ; Thu, 17 Dec 2020 02:49:06 -0800 (PST) Received: by mail-ed1-x533.google.com with SMTP id b2so28180378edm.3 for ; Thu, 17 Dec 2020 02:49:06 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=jlu9YbCN+xfICT/JHvGlkfpb81Fg0+Bwk3beGhrNPiw=; b=kQ3mBU2A7lUDVBNP8yRDt3btPnEiLw6T6ksbE0oUVE7uD4AL1VJUPHqmZfFojJAavk b2PsOCEEcpC/fH/FE5zLmMl0ZOhuWuV0c1db3vyDfKWtbDYm4PQoYuSqwq7XpcWeCFq2 LydprRMtKdgZgdQtuqcFU0pxwmUqWUB+JJ/0QeUHJLfAICUcrHxJfBnpK6+Q6mI0XQgH y0mERnTItVCe11ymIATF+wLOcEJ/Ig2g+BylbhqN4kaUEo3xgk2adwkcp/ZzQEJ0K2XH wcixbyEbG1PLAJIP2YKqCbOjG6SVNQLp4xz0SHVjAkbucXBr5WF7SV37qD48EaaN6eIs 91Ew== 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=jlu9YbCN+xfICT/JHvGlkfpb81Fg0+Bwk3beGhrNPiw=; b=lbgv3lxbmRUR7pwdrHFiPXyI9oFxMDEsqx0m2evbXwIVTUfIy7ofPZRsPCw4xvJd0J 4tSmM2MafqwYz4QJL+w63L/VWZ92NfXzlG7DXAeadBM2heFEIFWJnWLa1NxJF2vhR1Um bNjqB1BldUF3KxcWjRW1TXlLxUJ5vLXla66bvt2whIFl+7u0WyMaMlHLyBIMLKnqmrL6 XsaEAP/NNiepYTmmDsGVLTRWhZnBMfCaNEGvIi6YVtEvtIVyLrIrvSaVu1RPobLt3OaU fLZGIH2g9TyREgkLl5+J4+Uqa5GU/YA0YeDvrYq/UgQMA1fTtODU8PFLN9msrri6XAO9 DJNw== X-Gm-Message-State: AOAM533BQ1MvABXz76aY+ax9Y8paj31Is9DOwX+IRyVH3m4GFhGe5JS0 35yaOmZtYxHX1DxQBDaq4qh+Tv15GCPeNpcMjfCoow== X-Google-Smtp-Source: ABdhPJz5RsUSEq4LXUEu+gfDETPHdfWF2gjImVecob/CD0EldRDfVC4tj9PvGcLX4A9AW/SaCcTttdQEdLjhxB23uYk= X-Received: by 2002:a05:6402:229b:: with SMTP id cw27mr37587049edb.23.1608202143684; Thu, 17 Dec 2020 02:49:03 -0800 (PST) MIME-Version: 1.0 References: <20201216160330.GG2657@paulmck-ThinkPad-P72> In-Reply-To: <20201216160330.GG2657@paulmck-ThinkPad-P72> From: Naresh Kamboju Date: Thu, 17 Dec 2020 16:18:52 +0530 Message-ID: Subject: Re: i386: rcu-torture: WARNING: at kernel/rcu/rcutorture.c:1169 rcu_torture_writer [rcutorture] To: "Paul E. McKenney" Cc: rcu@vger.kernel.org, Linux-Next Mailing List , open list , lkft-triage@lists.linaro.org, Peter Zijlstra , Jakub Kicinski , Greg Kroah-Hartman , Thomas Gleixner Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Paul, Thanks for your inputs. On Wed, 16 Dec 2020 at 21:33, Paul E. McKenney wrote: > > On Wed, Dec 16, 2020 at 03:40:04PM +0530, Naresh Kamboju wrote: > > Linux Kernel Functional Testing (LKFT) started running rcu-torture tests on > > qemu_arm64, qemu_arm qemu_x86_64 and qemu_i386 from our CI build systems. > > > > The following warning(s) noticed on qemu_i386 while running rcu-torture test > > on Linux mainline and Linux -next master branch. Since we do not have baseline > > results i can not comment this as regression but when compared with > > stable-rc 5.4 kernel this warning is new on mainline and next. > > The rcutorture testing "stutters", that is, it periodically intentionally > drops the test load down to zero for a few seconds. The expectation is > that with no load, rcutorture will have no trouble finishing any needed > grace periods within that zero-load period. If at the end of the stutter > period, RCU work remains undone, then this warning is emitted. > > This warning can be a false positive in the following situations: > > 1. The system on which you are running rcutorture is under > additional heavy load. The DUT is running the test - rcutorture - only. > 2. You are running multiple guest OSes, each of which is running > rcutorture, and vCPUs from each of the guest OSes ends up > sharing a core with a vCPU from one of the other guests. This > can cause the zero-load period to not be so unloaded. > > 3. You built rcutorture into your kernel, so that rcutorture starts > immediately at boot time (CONFIG_RCU_TORTURE_TEST=y). If your > boot takes long enough, rcutorture can massively overload the > single boot CPU, which can in turn result in this warning. The test was built as a module. CONFIG_RCU_TORTURE_TEST=m > > If you are in situation #1, I suggest disabling stuttering using the > rcutorture.stutter=0 kernel boot parameter. > > If you are in situation #2, I suggest binding the guest-OS vCPUs > to avoid them sharing cores with each other. > > If you are in situation #3, I have patches that I expect to submit > upstream in the v5.12 merge window that can help. Hey, they work for me! > If you would like to test them before then, please let me know. > > If something else is going on, please let me know what it is so that > I can fix it one way or another. We were running on qemu_i386 today. I have tested on real hardware and the reported problem has been reproduced. > This warning has been present for quite some time, but I continually > make rcutorture more aggressive, and this could well be part of the > fallout of additional rcutorture aggression. > > And either way, thank you for trying out rcutorture! We are happy to test :) - Naresh