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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C8DC4C433F5 for ; Wed, 10 Nov 2021 15:21:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AA16A6115B for ; Wed, 10 Nov 2021 15:21:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232111AbhKJPXt (ORCPT ); Wed, 10 Nov 2021 10:23:49 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]:49109 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231488AbhKJPXt (ORCPT ); Wed, 10 Nov 2021 10:23:49 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1636557661; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Lhjq4wAJfTAQzB4aUh8/HWQOCKwr9ITogKZbi8YswJA=; b=i/HnP+j9EaFVfwS3UGABgU+7UWyvEboiNAwF4zoBZzulT8KFitAK+ZyIDgmKGrzpGC+vH/ v2ATCj14b4xuYIbwAxqAXnZ2mEIoo4WVIbzZ3j8so81xYfw/uHy4YUo8jt53n3tWqR60hA aMlYuVkw7u35u2QuJZqJFuz/Ua/viXo= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-105-QeCXEl5YPDetK4CXDZDdEg-1; Wed, 10 Nov 2021 10:20:57 -0500 X-MC-Unique: QeCXEl5YPDetK4CXDZDdEg-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id DE4291B18BD3; Wed, 10 Nov 2021 15:20:54 +0000 (UTC) Received: from [10.22.11.131] (unknown [10.22.11.131]) by smtp.corp.redhat.com (Postfix) with ESMTP id 13BDC56A87; Wed, 10 Nov 2021 15:20:30 +0000 (UTC) Message-ID: Date: Wed, 10 Nov 2021 10:20:29 -0500 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.2.0 Subject: Re: [PATCH v8 0/6] cgroup/cpuset: Add new cpuset partition type & empty effecitve cpus Content-Language: en-US To: Felix Moessbauer Cc: 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, mkoutny@suse.com, mtosatti@redhat.com, pauld@redhat.com, peterz@infradead.org, shuah@kernel.org, tj@kernel.org, jan.kiszka@siemens.com, henning.schild@siemens.com References: <20211018143619.205065-1-longman@redhat.com> <20211110111357.17617-1-felix.moessbauer@siemens.com> From: Waiman Long In-Reply-To: <20211110111357.17617-1-felix.moessbauer@siemens.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On 11/10/21 06:13, Felix Moessbauer wrote: > Hi Weiman, > >> v8: >> - Reorganize the patch series and rationalize the features and >> constraints of a partition. >> - Update patch descriptions and documentation accordingly. >> >> v7: >> - Simplify the documentation patch (patch 5) as suggested by Tejun. >> - Fix a typo in patch 2 and improper commit log in patch 3. >> >> v6: >> - Remove duplicated tmpmask from update_prstate() which should fix the >> frame size too large problem reported by kernel test robot. >> >> This patchset makes four enhancements to the cpuset v2 code. >> >> Patch 1: Enable partition with no task to have empty cpuset.cpus.effective. >> >> Patch 2: Refining the features and constraints of a cpuset partition >> clarifying what changes are allowed. >> >> Patch 3: Add a new partition state "isolated" to create a partition >> root without load balancing. This is for handling intermitten workloads >> that have a strict low latency requirement. > > I just tested this patch-series and can confirm that it works on 5.15.0-rc7-rt15 (PREEMT_RT). > > However, I was not able to see any latency improvements when using > cpuset.cpus.partition=isolated. > 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. > > Just some more general notes: > > Even with this new "isolated" type, it is still very tricky to get a similar > behavior as with isolcpus (as long as I don't miss something here): > > Consider an RT application that consists of a non-rt thread that should be floating > and a rt-thread that should be placed in the isolated domain. > 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). > > Theoretically, this could be done externally, but in case the application sets the > affinity mask manually, you run into a timing issue (setting affinities to CPUs > outside the current cpuset.cpus results in EINVAL). I believe the "isolated" type will have more benefit on non PREEMPT_RT kernel. Anyway, having the "isolated" type is just the first step. It should be equivalent to "isolcpus=domain". There are other patches floating that attempt to move some of the isolcpus=nohz features into cpuset as well. It is not there yet, but we should be able to have better dynamic cpu isolation down the road. Cheers, Longman