From mboxrd@z Thu Jan 1 00:00:00 1970 From: Waiman Long Subject: Re: [PATCH v8 0/6] cgroup/cpuset: Add new cpuset partition type & empty effecitve cpus Date: Wed, 10 Nov 2021 10:20:29 -0500 Message-ID: References: <20211018143619.205065-1-longman@redhat.com> <20211110111357.17617-1-felix.moessbauer@siemens.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: 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= Content-Language: en-US In-Reply-To: <20211110111357.17617-1-felix.moessbauer@siemens.com> List-ID: Content-Type: text/plain; charset="us-ascii"; format="flowed" 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 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