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a=rsa-sha256; c=relaxed/simple; d=codeaurora.org; s=default; t=1529384771; bh=u/s/sdA6kjjvB6aNykJ1nXPxKMoyQJwQRROY0fH9xi8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=iGvW7xpQkVDDRvqk3SVPiPmebcLu6rWD0f7ia38YRcq2fHjo/V3CVuNdaOJE35zSc EVKMdHTBcnr5wMg3rdXyvdh4EaJ232Eqj9RNVCF9D7PTB+uZCUi869YmIo/A60ho5t IdjrzSo0qIIyhZlcp3g0ztNys15ehVB+ctryftwc= DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org 25EFA6060A Authentication-Results: pdx-caf-mail.web.codeaurora.org; dmarc=none (p=none dis=none) header.from=codeaurora.org Authentication-Results: pdx-caf-mail.web.codeaurora.org; spf=none smtp.mailfrom=pkondeti@codeaurora.org Date: Tue, 19 Jun 2018 10:36:01 +0530 From: Pavan Kondeti To: Quentin Perret Cc: peterz@infradead.org, rjw@rjwysocki.net, gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, mingo@redhat.com, dietmar.eggemann@arm.com, morten.rasmussen@arm.com, chris.redpath@arm.com, patrick.bellasi@arm.com, valentin.schneider@arm.com, vincent.guittot@linaro.org, thara.gopinath@linaro.org, viresh.kumar@linaro.org, tkjos@google.com, joelaf@google.com, smuckle@google.com, adharmap@quicinc.com, skannan@quicinc.com, juri.lelli@redhat.com, edubezval@gmail.com, srinivas.pandruvada@linux.intel.com, currojerez@riseup.net, javi.merino@kernel.org Subject: Re: [RFC PATCH v3 09/10] sched/fair: Select an energy-efficient CPU on task wake-up Message-ID: <20180619050601.GA9208@codeaurora.org> References: <20180521142505.6522-1-quentin.perret@arm.com> <20180521142505.6522-10-quentin.perret@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180521142505.6522-10-quentin.perret@arm.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, May 21, 2018 at 03:25:04PM +0100, Quentin Perret wrote: > + if (cpumask_test_cpu(prev_cpu, &p->cpus_allowed)) > + prev_energy = best_energy = compute_energy(p, prev_cpu); > + else > + prev_energy = best_energy = ULONG_MAX; > + > + for_each_freq_domain(sfd) { > + unsigned long spare_cap, max_spare_cap = 0; > + int max_spare_cap_cpu = -1; > + unsigned long util; > + > + /* Find the CPU with the max spare cap in the freq. dom. */ > + for_each_cpu_and(cpu, freq_domain_span(sfd), sched_domain_span(sd)) { > + if (!cpumask_test_cpu(cpu, &p->cpus_allowed)) > + continue; > + > + if (cpu == prev_cpu) > + continue; > + > + /* Skip CPUs that will be overutilized */ > + util = cpu_util_wake(cpu, p) + task_util; > + cpu_cap = capacity_of(cpu); > + if (cpu_cap * 1024 < util * capacity_margin) > + continue; > + > + spare_cap = cpu_cap - util; > + if (spare_cap > max_spare_cap) { > + max_spare_cap = spare_cap; > + max_spare_cap_cpu = cpu; > + } > + } > + > + /* Evaluate the energy impact of using this CPU. */ > + if (max_spare_cap_cpu >= 0) { > + cur_energy = compute_energy(p, max_spare_cap_cpu); > + if (cur_energy < best_energy) { > + best_energy = cur_energy; > + best_energy_cpu = max_spare_cap_cpu; > + } > + } > + } > + > + /* > + * We pick the best CPU only if it saves at least 1.5% of the > + * energy used by prev_cpu. > + */ > + if ((prev_energy - best_energy) > (prev_energy >> 6)) > + return best_energy_cpu; > + > + return prev_cpu; > +} We are comparing the best_energy_cpu against prev_cpu even when prev_cpu can't accommodate the waking task. Is this intentional? Should not we discard the prev_cpu if it can't accommodate the task. This can potentially make a BIG task run on a lower capacity CPU until load balancer kicks in and corrects the situation. Thanks, Pavan -- Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc. Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project.