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SubjectRe: [PATCH v3 09/13] sched/fair: Let asymmetric cpu configurations balance at wake-up
On Mon, Jul 25, 2016 at 02:34:26PM +0100, Morten Rasmussen wrote:


Because I forgot _again_, I added:

/*
* Disable WAKE_AFFINE in the case where task @p doesn't fit in the
* capacity of either the waking CPU @cpu or the previous CPU @prev_cpu.
*
* In that case WAKE_AFFINE doesn't make sense and we'll let
* BALANCE_WAKE sort things out.
*/

> +static int wake_cap(struct task_struct *p, int cpu, int prev_cpu)
> +{
> + long min_cap, max_cap;
> +
> + min_cap = min(capacity_orig_of(prev_cpu), capacity_orig_of(cpu));
> + max_cap = cpu_rq(cpu)->rd->max_cpu_capacity;

There's a tiny hole here, which I'm fairly sure we don't care about. If
@p last ran on @prev_cpu before @prev_cpu was split from @rd this
doesn't 'work' right.

> + /* Minimum capacity is close to max, no need to abort wake_affine */
> + if (max_cap - min_cap < max_cap >> 3)
> + return 0;
> +
> + return min_cap * 1024 < task_util(p) * capacity_margin;
> +}
> +
> /*
> * select_task_rq_fair: Select target runqueue for the waking task in domains
> * that have the 'sd_flag' flag set. In practice, this is SD_BALANCE_WAKE,
> @@ -5389,7 +5414,8 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_f
>
> if (sd_flag & SD_BALANCE_WAKE) {
> record_wakee(p);
> - want_affine = !wake_wide(p) && cpumask_test_cpu(cpu, tsk_cpus_allowed(p));
> + want_affine = !wake_wide(p) && !wake_cap(p, cpu, prev_cpu)
> + && cpumask_test_cpu(cpu, tsk_cpus_allowed(p));
> }
>
> rcu_read_lock();
> --
> 1.9.1
>

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