From: Pavan Kondeti <pkondeti@codeaurora.org>
To: Quentin Perret <quentin.perret@arm.com>
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
Date: Tue, 19 Jun 2018 10:36:01 +0530 [thread overview]
Message-ID: <20180619050601.GA9208@codeaurora.org> (raw)
In-Reply-To: <20180521142505.6522-10-quentin.perret@arm.com>
On Mon, May 21, 2018 at 03:25:04PM +0100, Quentin Perret wrote:
<snip>
> + 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.
next prev parent reply other threads:[~2018-06-19 5:06 UTC|newest]
Thread overview: 80+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-21 14:24 [RFC PATCH v3 00/10] Energy Aware Scheduling Quentin Perret
2018-05-21 14:24 ` [RFC PATCH v3 01/10] sched: Relocate arch_scale_cpu_capacity Quentin Perret
2018-05-21 14:24 ` [RFC PATCH v3 02/10] sched/cpufreq: Factor out utilization to frequency mapping Quentin Perret
2018-05-21 14:24 ` [RFC PATCH v3 03/10] PM: Introduce an Energy Model management framework Quentin Perret
2018-06-06 13:12 ` Dietmar Eggemann
2018-06-06 14:37 ` Quentin Perret
2018-06-06 15:20 ` Juri Lelli
2018-06-06 15:29 ` Quentin Perret
2018-06-06 16:26 ` Quentin Perret
2018-06-07 15:58 ` Dietmar Eggemann
2018-06-08 13:39 ` Javi Merino
2018-06-08 15:47 ` Quentin Perret
2018-06-09 8:24 ` Javi Merino
2018-06-06 16:47 ` Juri Lelli
2018-06-06 16:59 ` Quentin Perret
2018-06-07 14:44 ` Juri Lelli
2018-06-07 15:19 ` Quentin Perret
2018-06-07 15:55 ` Dietmar Eggemann
2018-06-08 8:25 ` Quentin Perret
2018-06-08 9:36 ` Juri Lelli
2018-06-08 10:31 ` Quentin Perret
2018-06-08 12:39 ` Dietmar Eggemann
2018-06-08 13:11 ` Quentin Perret
2018-06-08 16:39 ` Dietmar Eggemann
2018-06-08 17:02 ` Quentin Perret
2018-06-07 16:04 ` Juri Lelli
2018-06-07 17:31 ` Quentin Perret
2018-06-09 8:13 ` Javi Merino
2018-06-19 11:07 ` Peter Zijlstra
2018-06-19 12:35 ` Quentin Perret
2018-06-19 11:31 ` Peter Zijlstra
2018-06-19 12:40 ` Quentin Perret
2018-06-19 11:34 ` Peter Zijlstra
2018-06-19 12:58 ` Quentin Perret
2018-06-19 13:23 ` Peter Zijlstra
2018-06-19 13:38 ` Quentin Perret
2018-06-19 14:16 ` Peter Zijlstra
2018-06-19 14:21 ` Peter Zijlstra
2018-06-19 14:30 ` Peter Zijlstra
2018-06-19 14:23 ` Quentin Perret
2018-05-21 14:24 ` [RFC PATCH v3 04/10] PM / EM: Expose the Energy Model in sysfs Quentin Perret
2018-06-19 12:16 ` Peter Zijlstra
2018-06-19 13:06 ` Quentin Perret
2018-05-21 14:25 ` [RFC PATCH v3 05/10] sched/topology: Reference the Energy Model of CPUs when available Quentin Perret
2018-06-07 14:44 ` Juri Lelli
2018-06-07 16:02 ` Quentin Perret
2018-06-07 16:29 ` Juri Lelli
2018-06-07 17:26 ` Quentin Perret
2018-06-19 12:26 ` Peter Zijlstra
2018-06-19 13:24 ` Quentin Perret
2018-06-19 16:20 ` Peter Zijlstra
2018-06-19 17:13 ` Quentin Perret
2018-06-19 18:42 ` Peter Zijlstra
2018-06-20 7:58 ` Quentin Perret
2018-05-21 14:25 ` [RFC PATCH v3 06/10] sched: Add over-utilization/tipping point indicator Quentin Perret
2018-06-19 7:01 ` Pavan Kondeti
2018-06-19 10:26 ` Dietmar Eggemann
2018-05-21 14:25 ` [RFC PATCH v3 07/10] sched/fair: Introduce an energy estimation helper function Quentin Perret
2018-06-08 10:30 ` Juri Lelli
2018-06-19 9:51 ` Pavan Kondeti
2018-06-19 9:53 ` Quentin Perret
2018-05-21 14:25 ` [RFC PATCH v3 08/10] sched: Lowest energy aware balancing sched_domain level pointer Quentin Perret
2018-05-21 14:25 ` [RFC PATCH v3 09/10] sched/fair: Select an energy-efficient CPU on task wake-up Quentin Perret
2018-06-08 10:24 ` Juri Lelli
2018-06-08 11:19 ` Quentin Perret
2018-06-08 11:59 ` Juri Lelli
2018-06-08 16:26 ` Quentin Perret
2018-06-19 5:06 ` Pavan Kondeti [this message]
2018-06-19 7:57 ` Quentin Perret
2018-06-19 8:41 ` Pavan Kondeti
2018-05-21 14:25 ` [RFC PATCH v3 10/10] arch_topology: Start Energy Aware Scheduling Quentin Perret
2018-06-19 9:18 ` Pavan Kondeti
2018-06-19 9:40 ` Quentin Perret
2018-06-19 9:47 ` Juri Lelli
2018-06-19 10:02 ` Quentin Perret
2018-06-19 10:19 ` Juri Lelli
2018-06-19 10:25 ` Quentin Perret
2018-06-19 10:31 ` Juri Lelli
2018-06-19 10:49 ` Quentin Perret
2018-06-01 9:29 ` [RFC PATCH v3 00/10] " Quentin Perret
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