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[61.68.227.232]) by smtp.gmail.com with ESMTPSA id i3sm463722pjd.33.2020.11.23.15.31.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 23 Nov 2020 15:31:52 -0800 (PST) Date: Tue, 24 Nov 2020 10:31:49 +1100 From: Balbir Singh To: Vineeth Pillai Cc: "Joel Fernandes (Google)" , Nishanth Aravamudan , Julien Desfossez , Peter Zijlstra , Tim Chen , 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: <20201123233149.GB8893@balbir-desktop> References: <20201117232003.3580179-1-joel@joelfernandes.org> <20201117232003.3580179-10-joel@joelfernandes.org> <20201122114442.GD110669@balbir-desktop> <2cb42831-5074-e0a9-9e2a-f2a880504026@linux.microsoft.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2cb42831-5074-e0a9-9e2a-f2a880504026@linux.microsoft.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Nov 23, 2020 at 07:31:31AM -0500, Vineeth Pillai wrote: > Hi Balbir, > > On 11/22/20 6:44 AM, Balbir Singh wrote: > > > > This seems cumbersome, is there no way to track the min_vruntime via > > rq->core->min_vruntime? > Do you mean to have a core wide min_vruntime? We had a > similar approach from v3 to v7 and it had major issues which > broke the assumptions of cfs. There were some lengthy > discussions and Peter explained in-depth about the issues: > > https://lwn.net/ml/linux-kernel/20200506143506.GH5298@hirez.programming.kicks-ass.net/ > https://lwn.net/ml/linux-kernel/20200515103844.GG2978@hirez.programming.kicks-ass.net/ > One of the equations in the link is ">From which immediately follows that: T_k + T_l S_k+l = --------- (13) W_k + W_l On which we can define a combined lag: lag_k+l(i) := S_k+l - s_i (14) And that gives us the tools to compare tasks across a combined runqueue. " S_k+l reads like rq->core->vruntime, but it sounds like the equivalent of rq->core->vruntime is updated when we enter forced idle as opposed to all the time. Balbir