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Thu, 18 Jan 2024 04:53:01 -0800 (PST) X-Google-Smtp-Source: AGHT+IH7As1BDqXY9resBjb7KtzVWa0wxxWHCvwG2FLi7KKlmWPYt9Q+Y1u/l56Ffk5pU4XqKV6msA== X-Received: by 2002:a05:620a:2415:b0:783:3cdf:7e36 with SMTP id d21-20020a05620a241500b007833cdf7e36mr2106174qkn.58.1705582381434; Thu, 18 Jan 2024 04:53:01 -0800 (PST) Received: from localhost.localdomain ([151.29.130.8]) by smtp.gmail.com with ESMTPSA id he23-20020a05622a601700b0042a09928c10sm2114740qtb.33.2024.01.18.04.53.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 18 Jan 2024 04:53:01 -0800 (PST) Date: Thu, 18 Jan 2024 13:52:57 +0100 From: Juri Lelli To: Tejun Heo Cc: Waiman Long , Lai Jiangshan , Aaron Tomlin , Valentin Schneider , linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH 3/4] kernel/workqueue: Distinguish between general unbound and WQ_SYSFS cpumask changes Message-ID: References: <20240116161929.232885-1-juri.lelli@redhat.com> <20240116161929.232885-4-juri.lelli@redhat.com> <72e4a971-96e5-44b7-b348-bbdb68e54b40@redhat.com> 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: On 17/01/24 09:42, Tejun Heo wrote: > Hello, > > On Wed, Jan 17, 2024 at 02:32:34PM -0500, Waiman Long wrote: > > My impression is that changing the workqueue cpumask of ordered unbound > > workqueue may break the ordering guarantee momentarily. I was planning to > > Ah, you're right. Changing cpumask would require changing the dfl_pwq and > that can introduce extra concurrency and break ordering and it's exempt from > unbound_cpumask updates. We likely need to add a mechanism for updating > ordered wq's so that the new pwq doesn't become until the previous one is > drained. Thanks for the additional info! Guess I'll need to think more about this and possibly coordinate the effort with Waiman. Best, Juri