Re: [PATCH v4 1/4] sched/fair: Add asymmetric CPU capacity wakeup scan

[Pavan Kondeti <pkondeti@codeaurora.org>]

On Thu, Feb 06, 2020 at 07:19:54PM +0000, Valentin Schneider wrote:
> From: Morten Rasmussen <morten.rasmussen@arm.com>
> 

<snip>

> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index fe4e0d7753756..9a5a6e9d2375e 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5894,6 +5894,40 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
>  	return cpu;
>  }
>  
> +/*
> + * Scan the asym_capacity domain for idle CPUs; pick the first idle one on which
> + * the task fits. If no CPU is big enough, but there are idle ones, try to
> + * maximize capacity.
> + */
> +static int
> +select_idle_capacity(struct task_struct *p, struct sched_domain *sd, int target)
> +{
> +	unsigned long best_cap = 0;
> +	int cpu, best_cpu = -1;
> +	struct cpumask *cpus;
> +
> +	sync_entity_load_avg(&p->se);
> +
> +	cpus = this_cpu_cpumask_var_ptr(select_idle_mask);
> +	cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr);
> +
> +	for_each_cpu_wrap(cpu, cpus, target) {
> +		unsigned long cpu_cap = capacity_of(cpu);
> +
> +		if (!available_idle_cpu(cpu) && !sched_idle_cpu(cpu))
> +			continue;
> +		if (task_fits_capacity(p, cpu_cap))
> +			return cpu;
> +
> +		if (cpu_cap > best_cap) {
> +			best_cap = cpu_cap;
> +			best_cpu = cpu;
> +		}
> +	}
> +
> +	return best_cpu;
> +}
> +
>  /*
>   * Try and locate an idle core/thread in the LLC cache domain.
>   */
> @@ -5902,6 +5936,28 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
>  	struct sched_domain *sd;
>  	int i, recent_used_cpu;
>  
> +	/*
> +	 * For asymmetric CPU capacity systems, our domain of interest is
> +	 * sd_asym_cpucapacity rather than sd_llc.
> +	 */
> +	if (static_branch_unlikely(&sched_asym_cpucapacity)) {
> +		sd = rcu_dereference(per_cpu(sd_asym_cpucapacity, target));
> +		/*
> +		 * On an asymmetric CPU capacity system where an exclusive
> +		 * cpuset defines a symmetric island (i.e. one unique
> +		 * capacity_orig value through the cpuset), the key will be set
> +		 * but the CPUs within that cpuset will not have a domain with
> +		 * SD_ASYM_CPUCAPACITY. These should follow the usual symmetric
> +		 * capacity path.
> +		 */
> +		if (!sd)
> +			goto symmetric;
> +
> +		i = select_idle_capacity(p, sd, target);
> +		return ((unsigned)i < nr_cpumask_bits) ? i : target;
> +	}
> +
> +symmetric:
>  	if (available_idle_cpu(target) || sched_idle_cpu(target))
>  		return target;
>  
> -- 
> 2.24.0
> 

Looks good to me.

Thanks,
Pavan

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