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From: Quentin Perret <quentin.perret@arm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: rjw@rjwysocki.net, linux-kernel@vger.kernel.org,
	linux-pm@vger.kernel.org, gregkh@linuxfoundation.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,
	joel@joelfernandes.org, smuckle@google.com, adharmap@quicinc.com,
	skannan@quicinc.com, pkondeti@codeaurora.org,
	juri.lelli@redhat.com, edubezval@gmail.com,
	srinivas.pandruvada@linux.intel.com, currojerez@riseup.net,
	javi.merino@kernel.org
Subject: Re: [PATCH v5 12/14] sched/fair: Select an energy-efficient CPU on task wake-up
Date: Thu, 2 Aug 2018 17:21:34 +0100
Message-ID: <20180802162132.7ur5poka5m7r2io2@queper01-lin> (raw)
In-Reply-To: <20180802135426.GX2476@hirez.programming.kicks-ass.net>

On Thursday 02 Aug 2018 at 15:54:26 (+0200), Peter Zijlstra wrote:
> On Tue, Jul 24, 2018 at 01:25:19PM +0100, Quentin Perret wrote:
> > @@ -6385,18 +6492,26 @@ static int
> >  select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_flags)
> >  {
> >  	struct sched_domain *tmp, *sd = NULL;
> > +	struct freq_domain *fd;
> >  	int cpu = smp_processor_id();
> >  	int new_cpu = prev_cpu;
> > -	int want_affine = 0;
> > +	int want_affine = 0, want_energy = 0;
> >  	int sync = (wake_flags & WF_SYNC) && !(current->flags & PF_EXITING);
> >  
> > +	rcu_read_lock();
> >  	if (sd_flag & SD_BALANCE_WAKE) {
> >  		record_wakee(p);
> > -		want_affine = !wake_wide(p) && !wake_cap(p, cpu, prev_cpu)
> > -			      && cpumask_test_cpu(cpu, &p->cpus_allowed);
> > +		fd = rd_freq_domain(cpu_rq(cpu)->rd);
> > +		want_energy = fd && !READ_ONCE(cpu_rq(cpu)->rd->overutilized);
> > +		want_affine = !wake_wide(p) && !wake_cap(p, cpu, prev_cpu) &&
> > +			      cpumask_test_cpu(cpu, &p->cpus_allowed);
> > +	}
> > +
> > +	if (want_energy) {
> > +		new_cpu = find_energy_efficient_cpu(p, prev_cpu, fd);
> > +		goto unlock;
> >  	}
> >  
> 
> And I suppose you rely on the compiler to optimize that for the static
> key inside rd_freq_domain()... Does it do a good job of that?

I does for sure when CONFIG_ENERGY_MODEL=n since rd_freq_domain() is
stubbed to false, but that's an easy one ;-)

> 
> That is, would not something like:
> 
> 
> 	rcu_read_lock();
> 	if (sd_flag & SD_BALANCE_WAKE) {
> 		record_wakee(p);
> 
> 		if (static_branch_unlikely(&sched_energy_present)) {
> 			struct root_domain *rd = cpu_rq(cpu)->rd;
> 			struct freq_domain *fd = rd_freq_domain(rd);
> 
> 			if (fd && !READ_ONCE(rd->overutilized)) {
> 				new_cpu = find_energy_efficient_cpu(p, prev_cpu, fd);
> 				goto unlock;
> 			}
> 		}
> 
> 		/* ... */
> 	}
> 
> 
> Be far more clear ?

It is clearer. Having the static key check in rd_freq_domain() makes
the change to find_busiest_group() smaller, but I can totally change it
with something like the above.

I'll do that in v6.

Thanks,
Quentin

  reply index

Thread overview: 72+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-07-24 12:25 [PATCH v5 00/14] Energy Aware Scheduling Quentin Perret
2018-07-24 12:25 ` [PATCH v5 01/14] sched: Relocate arch_scale_cpu_capacity Quentin Perret
2018-07-24 12:25 ` [PATCH v5 02/14] sched/cpufreq: Factor out utilization to frequency mapping Quentin Perret
2018-07-24 12:25 ` [PATCH v5 03/14] PM: Introduce an Energy Model management framework Quentin Perret
2018-08-09 21:52   ` Rafael J. Wysocki
2018-08-10  8:15     ` Quentin Perret
2018-08-10  8:41       ` Rafael J. Wysocki
2018-08-10  9:12         ` Quentin Perret
2018-08-10 11:13           ` Rafael J. Wysocki
2018-08-10 12:30             ` Quentin Perret
2018-08-12  9:49               ` Rafael J. Wysocki
2018-07-24 12:25 ` [PATCH v5 04/14] PM / EM: Expose the Energy Model in sysfs Quentin Perret
2018-07-24 12:25 ` [PATCH v5 05/14] sched/topology: Reference the Energy Model of CPUs when available Quentin Perret
2018-07-24 12:25 ` [PATCH v5 06/14] sched/topology: Lowest energy aware balancing sched_domain level pointer Quentin Perret
2018-07-26 16:00   ` Valentin Schneider
2018-07-26 17:01     ` Quentin Perret
2018-07-24 12:25 ` [PATCH v5 07/14] sched/topology: Introduce sched_energy_present static key Quentin Perret
2018-07-24 12:25 ` [PATCH v5 08/14] sched/fair: Clean-up update_sg_lb_stats parameters Quentin Perret
2018-07-24 12:25 ` [PATCH v5 09/14] sched: Add over-utilization/tipping point indicator Quentin Perret
2018-08-02 12:26   ` Peter Zijlstra
2018-08-02 13:03     ` Quentin Perret
2018-08-02 13:08       ` Peter Zijlstra
2018-08-02 13:18         ` Quentin Perret
2018-08-02 13:48           ` Vincent Guittot
2018-08-02 14:14             ` Quentin Perret
2018-08-02 15:14               ` Vincent Guittot
2018-08-02 15:30                 ` Quentin Perret
2018-08-02 15:55                   ` Vincent Guittot
2018-08-02 16:00                     ` Quentin Perret
2018-08-02 16:07                       ` Vincent Guittot
2018-08-02 16:10                         ` Quentin Perret
2018-08-02 16:38                           ` Vincent Guittot
2018-08-02 16:59                             ` Quentin Perret
2018-08-03  7:48                               ` Vincent Guittot
2018-08-03  8:18                                 ` Quentin Perret
2018-08-03 13:49                                   ` Vincent Guittot
2018-08-03 14:21                                     ` Vincent Guittot
2018-08-03 15:55                                     ` Quentin Perret
2018-08-06  8:40                                       ` Vincent Guittot
2018-08-06  9:43                                         ` Quentin Perret
2018-08-06 10:45                                           ` Vincent Guittot
2018-08-06 11:02                                             ` Quentin Perret
2018-08-06 10:08                                         ` Dietmar Eggemann
2018-08-06 10:33                                           ` Vincent Guittot
2018-08-06 12:29                                             ` Dietmar Eggemann
2018-08-06 12:37                                               ` Vincent Guittot
2018-08-06 13:20                                                 ` Dietmar Eggemann
2018-08-09  9:30   ` Vincent Guittot
2018-08-09  9:38     ` Quentin Perret
2018-07-24 12:25 ` [PATCH v5 10/14] sched/cpufreq: Refactor the utilization aggregation method Quentin Perret
2018-07-30 19:35   ` skannan
2018-07-31  7:59     ` Quentin Perret
2018-07-31 19:31       ` skannan
2018-08-01  7:32         ` Rafael J. Wysocki
2018-08-01  8:23           ` Quentin Perret
2018-08-01  8:35             ` Rafael J. Wysocki
2018-08-01  9:23               ` Quentin Perret
2018-08-01  9:40                 ` Rafael J. Wysocki
2018-08-02 13:04                 ` Peter Zijlstra
2018-08-02 15:39                   ` Quentin Perret
2018-08-03 13:04                     ` Quentin Perret
2018-08-02 12:33     ` Peter Zijlstra
2018-08-02 12:45       ` Peter Zijlstra
2018-08-02 15:21         ` Quentin Perret
2018-08-02 17:36           ` Peter Zijlstra
2018-08-03 12:42             ` Quentin Perret
2018-07-24 12:25 ` [PATCH v5 11/14] sched/fair: Introduce an energy estimation helper function Quentin Perret
2018-07-24 12:25 ` [PATCH v5 12/14] sched/fair: Select an energy-efficient CPU on task wake-up Quentin Perret
2018-08-02 13:54   ` Peter Zijlstra
2018-08-02 16:21     ` Quentin Perret [this message]
2018-07-24 12:25 ` [PATCH v5 13/14] OPTIONAL: arch_topology: Start Energy Aware Scheduling Quentin Perret
2018-07-24 12:25 ` [PATCH v5 14/14] OPTIONAL: cpufreq: dt: Register an Energy Model Quentin Perret

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