From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mathieu Desnoyers Subject: Re: [regression] cpuset: offlined CPUs removed from affinity masks Date: Wed, 19 Feb 2020 10:50:35 -0500 (EST) Message-ID: <59426509.702.1582127435733.JavaMail.zimbra@efficios.com> References: <1251528473.590671.1579196495905.JavaMail.zimbra@efficios.com> <1317969050.4131.1581955387909.JavaMail.zimbra@efficios.com> <20200219151922.GB698990@mtj.thefacebook.com> <1589496945.670.1582126985824.JavaMail.zimbra@efficios.com> <20200219154740.GD698990@mtj.thefacebook.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: DKIM-Filter: OpenDKIM Filter v2.10.3 mail.efficios.com CCD34249842 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=efficios.com; s=default; t=1582127435; bh=n5cHT89YZyqvy7ZJIr0GDRx3VH9Jg3ndn0oVBAB6nME=; h=Date:From:To:Message-ID:MIME-Version; b=CmPM8/EWqcMTIbi1mbdrVOPedy+TO3w3D66BhLXu7EBQJz/InhT+S9wuJ76gOKznf FrMGRQcZR2XJo1sLQSUwR29n8cRxJTP3QF2usBRcVgyIjelW2vJ+yf4wGGzjABmTm9 XDvuBRIBK9djAXHiX1yvM77F51JVkPHgwatvw5bS87zdCrgOqmcvi4/EyYNhcccpVZ 6SHL5al2i0pWjfUHghhCLaUihNKQZlQBQhYxxxnAKGyDHYQTOYadJ2GWKjIZaUyzL0 FCz5giEUKWpDSbfKoEFKL5vBVPZ2g6fdHB0jYLARjs33Z+ZwVW1bbddPAuujNxmK7L ydeAy0PBy2qVQ== In-Reply-To: <20200219154740.GD698990-146+VewaZzwNjtGbbfXrCEEOCMrvLtNR@public.gmane.org> Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii" To: Tejun Heo Cc: Li Zefan , cgroups , linux-kernel , Peter Zijlstra , Ingo Molnar , Valentin Schneider ----- On Feb 19, 2020, at 10:47 AM, Tejun Heo tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org wrote: > On Wed, Feb 19, 2020 at 10:43:05AM -0500, Mathieu Desnoyers wrote: >> The regression I'm talking about here is that CONFIG_CPUSET=y changes the >> behavior of the sched_setaffinify system call, which existed prior to >> cpusets. >> >> sched_setaffinity should behave in the same way for kernels configured with >> CONFIG_CPUSET=y or CONFIG_CPUSET=n. >> >> The fact that cpuset decides to irreversibly change the task affinity mask >> may not be considered a regression if it has always done that, but changing >> the behavior of sched_setaffinity seems to fit the definition of a regression. > > We generally use "regression" for breakages which weren't in past > versions but then appeared later. It has debugging implications > because if we know something is a regression, we generally can point > to the commit which introduced the bug either through examining the > history or bisection. > > It is a silly bug, for sure, but slapping regression name on it just > confuses rather than helping anything. I can look into figuring out the commit introducing this issue, which I suspect will be close to the introduction of CONFIG_CPUSET into the kernel (which was ages ago). I'll check and let you know. Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com 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,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 6226DC34047 for ; Wed, 19 Feb 2020 15:50:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 14E0524671 for ; Wed, 19 Feb 2020 15:50:39 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=efficios.com header.i=@efficios.com header.b="CmPM8/EW" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726717AbgBSPuh (ORCPT ); Wed, 19 Feb 2020 10:50:37 -0500 Received: from mail.efficios.com ([167.114.26.124]:36442 "EHLO mail.efficios.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726558AbgBSPuh (ORCPT ); Wed, 19 Feb 2020 10:50:37 -0500 Received: from localhost (localhost [127.0.0.1]) by mail.efficios.com (Postfix) with ESMTP id 0C68A249843; Wed, 19 Feb 2020 10:50:36 -0500 (EST) Received: from mail.efficios.com ([127.0.0.1]) by localhost (mail03.efficios.com [127.0.0.1]) (amavisd-new, port 10032) with ESMTP id JUDKRNvcXdxi; Wed, 19 Feb 2020 10:50:35 -0500 (EST) Received: from localhost (localhost [127.0.0.1]) by mail.efficios.com (Postfix) with ESMTP id CCD34249842; Wed, 19 Feb 2020 10:50:35 -0500 (EST) DKIM-Filter: OpenDKIM Filter v2.10.3 mail.efficios.com CCD34249842 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=efficios.com; s=default; t=1582127435; bh=n5cHT89YZyqvy7ZJIr0GDRx3VH9Jg3ndn0oVBAB6nME=; h=Date:From:To:Message-ID:MIME-Version; b=CmPM8/EWqcMTIbi1mbdrVOPedy+TO3w3D66BhLXu7EBQJz/InhT+S9wuJ76gOKznf FrMGRQcZR2XJo1sLQSUwR29n8cRxJTP3QF2usBRcVgyIjelW2vJ+yf4wGGzjABmTm9 XDvuBRIBK9djAXHiX1yvM77F51JVkPHgwatvw5bS87zdCrgOqmcvi4/EyYNhcccpVZ 6SHL5al2i0pWjfUHghhCLaUihNKQZlQBQhYxxxnAKGyDHYQTOYadJ2GWKjIZaUyzL0 FCz5giEUKWpDSbfKoEFKL5vBVPZ2g6fdHB0jYLARjs33Z+ZwVW1bbddPAuujNxmK7L ydeAy0PBy2qVQ== X-Virus-Scanned: amavisd-new at efficios.com Received: from mail.efficios.com ([127.0.0.1]) by localhost (mail03.efficios.com [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id L-1Q0gBfzK1s; Wed, 19 Feb 2020 10:50:35 -0500 (EST) Received: from mail03.efficios.com (mail03.efficios.com [167.114.26.124]) by mail.efficios.com (Postfix) with ESMTP id C4A90249835; Wed, 19 Feb 2020 10:50:35 -0500 (EST) Date: Wed, 19 Feb 2020 10:50:35 -0500 (EST) From: Mathieu Desnoyers To: Tejun Heo Cc: Li Zefan , cgroups , linux-kernel , Peter Zijlstra , Ingo Molnar , Valentin Schneider Message-ID: <59426509.702.1582127435733.JavaMail.zimbra@efficios.com> In-Reply-To: <20200219154740.GD698990@mtj.thefacebook.com> References: <1251528473.590671.1579196495905.JavaMail.zimbra@efficios.com> <1317969050.4131.1581955387909.JavaMail.zimbra@efficios.com> <20200219151922.GB698990@mtj.thefacebook.com> <1589496945.670.1582126985824.JavaMail.zimbra@efficios.com> <20200219154740.GD698990@mtj.thefacebook.com> Subject: Re: [regression] cpuset: offlined CPUs removed from affinity masks MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Originating-IP: [167.114.26.124] X-Mailer: Zimbra 8.8.15_GA_3901 (ZimbraWebClient - FF72 (Linux)/8.8.15_GA_3895) Thread-Topic: cpuset: offlined CPUs removed from affinity masks Thread-Index: S0iZuQsNrtd7VCZ5UFMGGpTw409R/w== Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ----- On Feb 19, 2020, at 10:47 AM, Tejun Heo tj@kernel.org wrote: > On Wed, Feb 19, 2020 at 10:43:05AM -0500, Mathieu Desnoyers wrote: >> The regression I'm talking about here is that CONFIG_CPUSET=y changes the >> behavior of the sched_setaffinify system call, which existed prior to >> cpusets. >> >> sched_setaffinity should behave in the same way for kernels configured with >> CONFIG_CPUSET=y or CONFIG_CPUSET=n. >> >> The fact that cpuset decides to irreversibly change the task affinity mask >> may not be considered a regression if it has always done that, but changing >> the behavior of sched_setaffinity seems to fit the definition of a regression. > > We generally use "regression" for breakages which weren't in past > versions but then appeared later. It has debugging implications > because if we know something is a regression, we generally can point > to the commit which introduced the bug either through examining the > history or bisection. > > It is a silly bug, for sure, but slapping regression name on it just > confuses rather than helping anything. I can look into figuring out the commit introducing this issue, which I suspect will be close to the introduction of CONFIG_CPUSET into the kernel (which was ages ago). I'll check and let you know. Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com