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[109.81.80.21]) by smtp.gmail.com with UTF8SMTPSA id ffacd0b85a97d-3a099ae0ca4sm9966523f8f.14.2025.05.05.02.25.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 05 May 2025 02:25:08 -0700 (PDT) Date: Mon, 5 May 2025 11:25:08 +0200 From: Michal Hocko To: Sebastian Andrzej Siewior Cc: Marco Crivellari , linux-kernel@vger.kernel.org, Tejun Heo , Lai Jiangshan , Thomas Gleixner , Frederic Weisbecker Subject: Re: [PATCH 0/4] Workqueue: rename system workqueue and add WQ_PERCPU Message-ID: References: <20250503082834.49413-1-marco.crivellari@suse.com> <20250505065121.dlEw6_SC@linutronix.de> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250505065121.dlEw6_SC@linutronix.de> On Mon 05-05-25 08:51:21, Sebastian Andrzej Siewior wrote: > On 2025-05-03 10:28:30 [+0200], Marco Crivellari wrote: > > Hi! > Hi, > > > This series is the follow up of the discussion from: > > "workqueue: Always use wq_select_unbound_cpu() for WORK_CPU_UNBOUND." > > https://lore.kernel.org/all/20250221112003.1dSuoGyc@linutronix.de/ > > > > 1) [P 1-2] system workqueue rename: > > > > system_wq is a per-CPU workqueue, but his name is not clear. > > system_unbound_wq is to be used when locality is not required. > > > > system_wq renamed in system_percpu_wq, while system_unbound_wq > > became system_dfl_wq. > > > > 2) [P 3] Introduction of WQ_PERCPU. > > > > This patch adds a new WQ_PERCPU flag to explicitly request the legacy > > per-CPU behavior. WQ_UNBOUND will be removed once the migration is > > complete. > > > > Every alloc_workqueue() caller should use one among WQ_PERCPU or > > WQ_UNBOUND. This is actually enforced warning if both or none of them > > are present at the same time. > > > > 3) [P 4] alloc_workqueue() callee should pass explicitly WQ_PERCPU. > > > > This patch ensures that every caller that needs per-cpu workqueue > > will explicitly require it, using the WQ_PERCPU flag. > > Sounds like a plan. > I assume the huge patches were made with coccinelle? Yes, this makes a lot of sense. I think it is worth mentioning why do we want/need to go through this major refactoring. From my POV this will help cpu isolation in a long term because it reduces unpredictable interference from pcp workers. -- Michal Hocko SUSE Labs