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[141.239.159.203]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-1f9eb320917sm103970405ad.75.2024.06.26.13.49.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 26 Jun 2024 13:49:23 -0700 (PDT) Sender: Tejun Heo Date: Wed, 26 Jun 2024 10:49:22 -1000 From: Tejun Heo To: Vincent Guittot Cc: Peter Zijlstra , torvalds@linux-foundation.org, mingo@redhat.com, juri.lelli@redhat.com, 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 Subject: Re: [PATCH 10/39] sched: Factor out update_other_load_avgs() from __update_blocked_others() Message-ID: References: <20240501151312.635565-1-tj@kernel.org> <20240501151312.635565-11-tj@kernel.org> <20240624123529.GM31592@noisy.programming.kicks-ass.net> Precedence: bulk X-Mailing-List: bpf@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: Hello, On Tue, Jun 25, 2024 at 11:13:54AM +0200, Vincent Guittot wrote: > > Hmm.... I think I saw RT's schedutil signal stuck high constantly pushing up > > the frequency. I might be mistaken tho. I'll check again. > > This is used when selecting a frequency for fair tasks When schedutil is used as the governor, sugov_get_util() provides the source utilization information to determine the target frequency. sugov_get_util() gets the CFS util metric from cpu_util_cfs_boost() and then runs it through effective_cpu_util(). effective_cpu_util() does a bunch of things including adding cpu_util_irq(), cpu_util_rt() and cpu_util_dl(), so if SCX doesn't decay these utilization metrics, they never decay and schedutil ends up making decisions with stale stuck-high numbers. I can easily confirm the behavior by sprinkling some trace_printks and commenting out update_other_load_avgs() on the SCX side. Thanks. -- tejun