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[90.233.213.186]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-52f0046ed98sm1366708e87.187.2024.07.24.07.23.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 24 Jul 2024 07:23:37 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Wed, 24 Jul 2024 16:23:35 +0200 To: Breno Leitao Cc: Waiman Long , "Paul E. McKenney" , Frederic Weisbecker , Neeraj Upadhyay , Joel Fernandes , Josh Triplett , Boqun Feng , Uladzislau Rezki , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Zqiang , rcu@vger.kernel.org, linux-kernel@vger.kernel.org, Vratislav Bendel Subject: Re: [PATCH] rcu: Use system_unbound_wq to avoid disturbing isolated CPUs Message-ID: References: <20240723181025.187413-1-longman@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 Wed, Jul 24, 2024 at 06:30:29AM -0700, Breno Leitao wrote: > On Tue, Jul 23, 2024 at 02:10:25PM -0400, Waiman Long wrote: > > It was discovered that isolated CPUs could sometimes be disturbed by > > kworkers processing kfree_rcu() works causing higher than expected > > latency. It is because the RCU core uses "system_wq" which doesn't have > > the WQ_UNBOUND flag to handle all its work items. Fix this violation of > > latency limits by using "system_unbound_wq" in the RCU core instead. > > This will ensure that those work items will not be run on CPUs marked > > as isolated. > > > > Beside the WQ_UNBOUND flag, the other major difference between system_wq > > and system_unbound_wq is their max_active count. The system_unbound_wq > > has a max_active of WQ_MAX_ACTIVE (512) while system_wq's max_active > > is WQ_DFL_ACTIVE (256) which is half of WQ_MAX_ACTIVE. > > > > Reported-by: Vratislav Bendel > > I've seen this problem a while ago and reported to the list: > > https://lore.kernel.org/all/Zp906X7VJGNKl5fW@gmail.com/ > > I've just applied this test, and run my workload for 2 hours without > hitting this issue. Thanks for solving it. > > Tested-by: Breno Leitao > Thank you for testing this! I saw your recent email about that :) -- Uladzislau Rezki