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[61.68.227.232]) by smtp.gmail.com with ESMTPSA id r66sm7633564pfc.114.2020.11.22.03.44.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 22 Nov 2020 03:44:46 -0800 (PST) Date: Sun, 22 Nov 2020 22:44:42 +1100 From: Balbir Singh To: "Joel Fernandes (Google)" Cc: Nishanth Aravamudan , Julien Desfossez , Peter Zijlstra , Tim Chen , Vineeth Pillai , Aaron Lu , Aubrey Li , tglx@linutronix.de, linux-kernel@vger.kernel.org, mingo@kernel.org, torvalds@linux-foundation.org, fweisbec@gmail.com, keescook@chromium.org, kerrnel@google.com, Phil Auld , Valentin Schneider , Mel Gorman , Pawan Gupta , Paolo Bonzini , vineeth@bitbyteword.org, Chen Yu , Christian Brauner , Agata Gruza , Antonio Gomez Iglesias , graf@amazon.com, konrad.wilk@oracle.com, dfaggioli@suse.com, pjt@google.com, rostedt@goodmis.org, derkling@google.com, benbjiang@tencent.com, Alexandre Chartre , James.Bottomley@hansenpartnership.com, OWeisse@umich.edu, Dhaval Giani , Junaid Shahid , jsbarnes@google.com, chris.hyser@oracle.com, Ben Segall , Josh Don , Hao Luo , Tom Lendacky , Aubrey Li , "Paul E. McKenney" , Tim Chen Subject: Re: [PATCH -tip 09/32] sched/fair: Snapshot the min_vruntime of CPUs on force idle Message-ID: <20201122114442.GD110669@balbir-desktop> References: <20201117232003.3580179-1-joel@joelfernandes.org> <20201117232003.3580179-10-joel@joelfernandes.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201117232003.3580179-10-joel@joelfernandes.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Nov 17, 2020 at 06:19:39PM -0500, Joel Fernandes (Google) wrote: > During force-idle, we end up doing cross-cpu comparison of vruntimes > during pick_next_task. If we simply compare (vruntime-min_vruntime) > across CPUs, and if the CPUs only have 1 task each, we will always > end up comparing 0 with 0 and pick just one of the tasks all the time. > This starves the task that was not picked. To fix this, take a snapshot > of the min_vruntime when entering force idle and use it for comparison. > This min_vruntime snapshot will only be used for cross-CPU vruntime > comparison, and nothing else. > > This resolves several performance issues that were seen in ChromeOS > audio usecase. > > NOTE: Note, this patch will be improved in a later patch. It is just > kept here as the basis for the later patch and to make rebasing > easier. Further, it may make reverting the improvement easier in > case the improvement causes any regression. > This seems cumbersome, is there no way to track the min_vruntime via rq->core->min_vruntime? Balbir Singh.