Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3E631C4332F for ; Wed, 10 Nov 2021 16:16:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1D41161241 for ; Wed, 10 Nov 2021 16:16:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230218AbhKJQTE (ORCPT ); Wed, 10 Nov 2021 11:19:04 -0500 Received: from gecko.sbs.de ([194.138.37.40]:50079 "EHLO gecko.sbs.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229473AbhKJQTD (ORCPT ); Wed, 10 Nov 2021 11:19:03 -0500 Received: from mail2.sbs.de (mail2.sbs.de [192.129.41.66]) by gecko.sbs.de (8.15.2/8.15.2) with ESMTPS id 1AAGFiIM029239 (version=TLSv1.2 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 10 Nov 2021 17:15:44 +0100 Received: from [167.87.75.31] ([167.87.75.31]) by mail2.sbs.de (8.15.2/8.15.2) with ESMTP id 1AAGFfna016041; Wed, 10 Nov 2021 17:15:41 +0100 Subject: Re: [PATCH v8 0/6] cgroup/cpuset: Add new cpuset partition type & empty effecitve cpus To: Marcelo Tosatti , "Moessbauer, Felix" Cc: =?UTF-8?Q?Michal_Koutn=c3=bd?= , "longman@redhat.com" , "akpm@linux-foundation.org" , "cgroups@vger.kernel.org" , "corbet@lwn.net" , "frederic@kernel.org" , "guro@fb.com" , "hannes@cmpxchg.org" , "juri.lelli@redhat.com" , "linux-doc@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-kselftest@vger.kernel.org" , "lizefan.x@bytedance.com" , "pauld@redhat.com" , "peterz@infradead.org" , "shuah@kernel.org" , "tj@kernel.org" , "henning.schild@siemens.com" References: <20211018143619.205065-1-longman@redhat.com> <20211110111357.17617-1-felix.moessbauer@siemens.com> <20211110135653.GD20566@blackbody.suse.cz> <20211110161020.GA20101@fuller.cnet> From: Jan Kiszka Message-ID: Date: Wed, 10 Nov 2021 17:15:41 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 MIME-Version: 1.0 In-Reply-To: <20211110161020.GA20101@fuller.cnet> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10.11.21 17:10, Marcelo Tosatti wrote: > On Wed, Nov 10, 2021 at 03:21:54PM +0000, Moessbauer, Felix wrote: >> >> >>> -----Original Message----- >>> From: Michal Koutný >>> Sent: Wednesday, November 10, 2021 2:57 PM >>> To: Moessbauer, Felix (T RDA IOT SES-DE) >>> Cc: longman@redhat.com; akpm@linux-foundation.org; >>> cgroups@vger.kernel.org; corbet@lwn.net; frederic@kernel.org; guro@fb.com; >>> hannes@cmpxchg.org; juri.lelli@redhat.com; linux-doc@vger.kernel.org; linux- >>> kernel@vger.kernel.org; linux-kselftest@vger.kernel.org; >>> lizefan.x@bytedance.com; mtosatti@redhat.com; pauld@redhat.com; >>> peterz@infradead.org; shuah@kernel.org; tj@kernel.org; Kiszka, Jan (T RDA >>> IOT) ; Schild, Henning (T RDA IOT SES-DE) >>> >>> Subject: Re: [PATCH v8 0/6] cgroup/cpuset: Add new cpuset partition type & >>> empty effecitve cpus >>> >>> Hello. >>> >>> On Wed, Nov 10, 2021 at 12:13:57PM +0100, Felix Moessbauer >>> wrote: >>>> However, I was not able to see any latency improvements when using >>>> cpuset.cpus.partition=isolated. >>> >>> Interesting. What was the baseline against which you compared it (isolcpus, no >>> cpusets,...)? >> >> For this test, I just compared both settings cpuset.cpus.partition=isolated|root. >> There, I did not see a significant difference (but I know, RT tuning depends on a ton of things). >> >>> >>>> The test was performed with jitterdebugger on CPUs 1-3 and the following >>> cmdline: >>>> rcu_nocbs=1-4 nohz_full=1-4 irqaffinity=0,5-6,11 intel_pstate=disable >>>> On the other cpus, stress-ng was executed to generate load. >>>> [...] >>> >>>> This requires cgroup.type=threaded on both cgroups and changes to the >>>> application (threads have to be born in non-rt group and moved to rt-group). >>> >>> But even with isolcpus the application would need to set affinity of threads to >>> the selected CPUs (cf cgroup migrating). Do I miss anything? >> >> Yes, that's true. But there are two differences (given that you use isolcpus): >> 1. the application only has to set the affinity for rt threads. >> Threads that do not explicitly set the affinity are automatically excluded from the isolated cores. >> Even common rt test applications like jitterdebugger do not pin their non-rt threads. >> 2. Threads can be started on non-rt CPUs and then bound to a specific rt CPU. >> This binding can be specified before thread creation via pthread_create. >> By that, you can make sure that at no point in time a thread has a "forbidden" CPU in its affinities. >> >> With cgroup2, you cannot guarantee the second aspect, as thread creation and moving to a cgroup is not an atomic operation. >> Also - please correct me if I'm wrong - you first have to create a thread before moving it into a group. >> At creation time, you cannot set the final affinity mask (as you create it in the non-rt group and there the CPU is not in the cpuset.cpus). >> Once you move the thread to the rt cgroup, it has a default mask and by that can be executed on other rt cores. > > man clone3: > > CLONE_NEWCGROUP (since Linux 4.6) > Create the process in a new cgroup namespace. If this flag is not set, then (as with fork(2)) the > process is created in the same cgroup namespaces as the calling process. > > For further information on cgroup namespaces, see cgroup_namespaces(7). > > Only a privileged process (CAP_SYS_ADMIN) can employ CLONE_NEWCGROUP. > Is there pthread_attr_setcgroup_np()? Jan -- Siemens AG, T RDA IOT Corporate Competence Center Embedded Linux