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([2601:188:c180:4250:ecbe:130d:668d:951d]) by smtp.gmail.com with ESMTPSA id 00721157ae682-71c058d6bf3sm398587b3.22.2025.08.08.09.27.25 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 08 Aug 2025 09:27:27 -0700 (PDT) From: Waiman Long X-Google-Original-From: Waiman Long Message-ID: <43af3cb0-3a8d-4ed4-9007-992475ba2844@redhat.com> Date: Fri, 8 Aug 2025 12:27:25 -0400 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 00/18] cgroup/cpuset: Enable runtime modification of To: Frederic Weisbecker Cc: Tejun Heo , Johannes Weiner , =?UTF-8?Q?Michal_Koutn=C3=BD?= , Jonathan Corbet , "Paul E. McKenney" , Neeraj Upadhyay , Joel Fernandes , Josh Triplett , Boqun Feng , Uladzislau Rezki , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Zqiang , Anna-Maria Behnsen , Ingo Molnar , Thomas Gleixner , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Ben Segall , Mel Gorman , Valentin Schneider , Shuah Khan , cgroups@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, rcu@vger.kernel.org, linux-kselftest@vger.kernel.org, Phil Auld , Costa Shulyupin , Gabriele Monaco , Cestmir Kalina References: <20250808151053.19777-1-longman@redhat.com> Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 8/8/25 11:50 AM, Frederic Weisbecker wrote: > Le Fri, Aug 08, 2025 at 11:10:44AM -0400, Waiman Long a écrit : >> The "nohz_full" and "rcu_nocbs" boot command parameters can be used to >> remove a lot of kernel overhead on a specific set of isolated CPUs which >> can be used to run some latency/bandwidth sensitive workloads with as >> little kernel disturbance/noise as possible. The problem with this mode >> of operation is the fact that it is a static configuration which cannot >> be changed after boot to adjust for changes in application loading. >> >> There is always a desire to enable runtime modification of the number >> of isolated CPUs that can be dedicated to this type of demanding >> workloads. This patchset is an attempt to do just that with an amount of >> CPU isolation close to what can be done with the nohz_full and rcu_nocbs >> boot kernel parameters. >> >> This patch series provides the ability to change the set of housekeeping >> CPUs at run time via the cpuset isolated partition functionality. >> Currently, the cpuset isolated partition is able to disable scheduler >> load balancing and the CPU affinity of the unbound workqueue to avoid the >> isolated CPUs. This patch series will extend that with other kernel noises >> associated with the nohz_full boot command line parameter which has the >> following sub-categories: >> - tick >> - timer >> - RCU >> - MISC >> - WQ >> - kthread > Thanks for working on that, I'm about to leave for 2 weeks vacation so I > won't have the time to check this until I'm back. > > However this series is highly conflicting with mine (cpuset/isolation: Honour > kthreads preferred affinity). Your patchset even redoes things I'm doing > (housekeeping cpumask update, RCU synchronization, HK_TYPE_DOMAIN to include > cpusets, etc...) > > I have a v2 that is almost ready to post. > > Wouldn't it be better to wait for it and its infrastructure changes before > proceeding with nohz_full? Sure. I am just posting this RFC patch series to show my current idea that I have. I will wait for your v2 and integrate on top. Looking forward to your upcoming v2 patch. Cheers, Longman