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[141.239.149.160]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-1fbb6ab75a8sm2201765ad.156.2024.07.08.12.30.38 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 08 Jul 2024 12:30:39 -0700 (PDT) Sender: Tejun Heo Date: Mon, 8 Jul 2024 09:30:38 -1000 From: Tejun Heo To: Peter Zijlstra Cc: torvalds@linux-foundation.org, mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, vschneid@redhat.com, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@kernel.org, joshdon@google.com, brho@google.com, pjt@google.com, derkling@google.com, haoluo@google.com, dvernet@meta.com, dschatzberg@meta.com, dskarlat@cs.cmu.edu, riel@surriel.com, changwoo@igalia.com, himadrics@inria.fr, memxor@gmail.com, andrea.righi@canonical.com, joel@joelfernandes.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, kernel-team@meta.com, Frederic Weisbecker Subject: Re: [PATCH sched_ext/for-6.11] sched_ext: Disallow loading BPF scheduler if isolcpus= domain isolation is in effect Message-ID: References: <20240501151312.635565-1-tj@kernel.org> <20240501151312.635565-10-tj@kernel.org> <20240624113212.GL31592@noisy.programming.kicks-ass.net> <20240625082926.GT31592@noisy.programming.kicks-ass.net> <20240626082342.GY31592@noisy.programming.kicks-ass.net> 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, Jun 26, 2024 at 03:27:02PM -1000, Tejun Heo wrote: > sched_domains regulate the load balancing for sched_classes. A machine can > be partitioned into multiple sections that are not load-balanced across > using either isolcpus= boot param or cpuset partitions. In such cases, tasks > that are in one partition are expected to stay within that partition. > > cpuset configured partitions are always reflected in each member task's > cpumask. As SCX always honors the task cpumasks, the BPF scheduler is > automatically in compliance with the configured partitions. > > However, for isolcpus= domain isolation, the isolated CPUs are simply > omitted from the top-level sched_domain[s] without further restrictions on > tasks' cpumasks, so, for example, a task currently running in an isolated > CPU may have more CPUs in its allowed cpumask while expected to remain on > the same CPU. > > There is no straightforward way to enforce this partitioning preemptively on > BPF schedulers and erroring out after a violation can be surprising. > isolcpus= domain isolation is being replaced with cpuset partitions anyway, > so keep it simple and simply disallow loading a BPF scheduler if isolcpus= > domain isolation is in effect. > > Signed-off-by: Tejun Heo > Link: http://lkml.kernel.org/r/20240626082342.GY31592@noisy.programming.kicks-ass.net > Cc: David Vernet > Cc: Peter Zijlstra > Cc: Frederic Weisbecker Applied to cgroup/for-6.11. Thanks. -- tejun