linux-kernel - Re: [PATCH v3 6/7] sched/fair: Remove task_util from effective utilization in feec()

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Date:   Tue, 22 Mar 2022 10:25:45 +0100
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Vincent Donnefort <vincent.donnefort@....com>,
        peterz@...radead.org, mingo@...hat.com, vincent.guittot@...aro.org
Cc:     linux-kernel@...r.kernel.org, morten.rasmussen@....com,
        chris.redpath@....com, qperret@...gle.com
Subject: Re: [PATCH v3 6/7] sched/fair: Remove task_util from effective
 utilization in feec()

On 08/03/2022 19:19, Vincent Donnefort wrote:

[...]

> Signed-off-by: Vincent Donnefort <vincent.donnefort@....com>

LGTM, just a couple of small remarks.

[...]

> @@ -6681,9 +6735,11 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
>  	unsigned long prev_delta = ULONG_MAX, best_delta = ULONG_MAX;
>  	struct root_domain *rd = cpu_rq(smp_processor_id())->rd;

s/cpu_rq(smp_processor_id())/this_rq()

Maybe you can clean this up with this patch?

>  	int cpu, best_energy_cpu = prev_cpu, target = -1;
> -	unsigned long cpu_cap, util, base_energy = 0;
> +	unsigned long cpu_cap, cpu_thermal_cap, util;

cpu_cap, cpu_thermal_cap and util can be defined inside the
`for (; pd; pd = pd->next)` scope below.

[...]

> @@ -6706,6 +6762,8 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
>  	if (!task_util_est(p))
>  		goto unlock;
>  
> +	eenv_task_busy_time(&eenv, p, prev_cpu);
> +
>  	for (; pd; pd = pd->next) {
>  		unsigned long cur_delta, spare_cap, max_spare_cap = 0;

cpu_cap and spare_cap could be combined into one to save on local
variables. E.g. cpu_cap

@@ -6908,8 +6908,6 @@ static int find_energy_efficient_cpu(struct
task_struct *p, int prev_cpu)
                         util = cpu_util_next(cpu, p, cpu);
                        cpu_cap = capacity_of(cpu);
-                       spare_cap = cpu_cap;
-                       lsub_positive(&spare_cap, util);
                         /*
                         * Skip CPUs that cannot satisfy the capacity
request.
@@ -6922,15 +6920,14 @@ static int find_energy_efficient_cpu(struct
task_struct *p, int prev_cpu)
                        if (!fits_capacity(util, cpu_cap))
                                continue;
 +                       lsub_positive(&cpu_cap, util);
+
                        if (cpu == prev_cpu) {
                                /* Always use prev_cpu as a candidate. */
                                compute_prev_delta = true;
-                       } else if (spare_cap > max_spare_cap) {
-                               /*
-                                * Find the CPU with the maximum spare
capacity
-                                * in the performance domain.
-                                */
-                               max_spare_cap = spare_cap;
+                       } else if (cpu_cap > max_spare_cap) {
+                                /* Find CPU with max spare capacity in
PD. */
+                               max_spare_cap = cpu_cap;
                                max_spare_cap_cpu = cpu;
                        }

[...]