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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT 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 356ABC004D3 for ; Wed, 24 Oct 2018 11:21:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DDB09207DD for ; Wed, 24 Oct 2018 11:21:58 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DDB09207DD Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=techsingularity.net Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727653AbeJXTtk (ORCPT ); Wed, 24 Oct 2018 15:49:40 -0400 Received: from outbound-smtp04.blacknight.com ([81.17.249.35]:39951 "EHLO outbound-smtp04.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727000AbeJXTtk (ORCPT ); Wed, 24 Oct 2018 15:49:40 -0400 Received: from mail.blacknight.com (pemlinmail05.blacknight.ie [81.17.254.26]) by outbound-smtp04.blacknight.com (Postfix) with ESMTPS id DD33A98A44 for ; Wed, 24 Oct 2018 11:21:54 +0000 (UTC) Received: (qmail 6832 invoked from network); 24 Oct 2018 11:21:54 -0000 Received: from unknown (HELO techsingularity.net) (mgorman@techsingularity.net@[37.228.229.142]) by 81.17.254.9 with ESMTPSA (AES256-SHA encrypted, authenticated); 24 Oct 2018 11:21:54 -0000 Date: Wed, 24 Oct 2018 12:21:53 +0100 From: Mel Gorman To: Srikar Dronamraju Cc: Peter Zijlstra , Ingo Molnar , LKML , Rik van Riel , Yi Wang , zhong.weidong@zte.com.cn, Yi Liu , Frederic Weisbecker , Thomas Gleixner Subject: Re: [PATCH v2] sched/core: Don't mix isolcpus and housekeeping CPUs Message-ID: <20181024112153.GD23537@techsingularity.net> References: <1540350169-18581-1-git-send-email-srikar@linux.vnet.ibm.com> <20181024085636.GB23537@techsingularity.net> <20181024094646.GA18466@linux.vnet.ibm.com> <20181024101508.GP3109@worktop.c.hoisthospitality.com> <20181024104124.GC18466@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20181024104124.GC18466@linux.vnet.ibm.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 24, 2018 at 04:11:24PM +0530, Srikar Dronamraju wrote: > * Peter Zijlstra [2018-10-24 12:15:08]: > > > On Wed, Oct 24, 2018 at 03:16:46PM +0530, Srikar Dronamraju wrote: > > > * Mel Gorman [2018-10-24 09:56:36]: > > > > > > > On Wed, Oct 24, 2018 at 08:32:49AM +0530, Srikar Dronamraju wrote: > > > > It would certainly be a bit odd because the > > > > application is asking for some protection but no guarantees are given > > > > and the application is not made aware via an error code that there is a > > > > problem. Asking the application to parse dmesg hoping to find the right > > > > error message is going to be fragile. > > > > > > Its a actually a good question. > > > What should we be doing if a mix of isolcpus and housekeeping (aka > > > non-isolcpus) is given in the mask. > > > > > > Right now as you pointed, there is no easy way for the application to know > > > which are the non-isolcpus to set its affinity. cpusets effective_cpus and > > > cpus_allowed both will contain isolcpus too. > > > > The easy option is to not use isolcpus :-) It is a horrifically bad > > interface. > > Agree, but thats something thats been exposed long time back. > Do we have an option to remove that? Hopefully nobody is using it. > I occasionally see bugs asking questions about interference from the kernel when isolcpus are in use. The last one was related to a timer interrupt every HZ (not a mainline kernel) but still, it's some evidence that it has users :( -- Mel Gorman SUSE Labs