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Date: Fri, 25 Aug 2017 15:40:47 +0200
From: Vincent Guittot <vincent.guittot@...aro.org>
To: Brendan Jackman <brendan.jackman@....com>
Cc: Ingo Molnar <mingo@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
linux-kernel <linux-kernel@...r.kernel.org>,
Joel Fernandes <joelaf@...gle.com>,
Andres Oportus <andresoportus@...gle.com>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Josef Bacik <josef@...icpanda.com>,
Morten Rasmussen <morten.rasmussen@....com>
Subject: Re: [PATCH v2 1/5] sched/fair: Move select_task_rq_fair slow-path
into its own function
On 25 August 2017 at 12:16, Brendan Jackman <brendan.jackman@....com> wrote:
> In preparation for changes that would otherwise require adding a new
> level of indentation to the while(sd) loop, create a new function
> find_idlest_cpu which contains this loop, and rename the existing
> find_idlest_cpu to find_idlest_group_cpu.
>
> Code inside the while(sd) loop is unchanged. @new_cpu is added as a
> variable in the new function, with the same initial value as the
> @new_cpu in select_task_rq_fair.
>
> Suggested-by: Peter Zijlstra <peterz@...radead.org>
> Signed-off-by: Brendan Jackman <brendan.jackman@....com>
> Cc: Dietmar Eggemann <dietmar.eggemann@....com>
> Cc: Vincent Guittot <vincent.guittot@...aro.org>
> Cc: Josef Bacik <josef@...icpanda.com>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Morten Rasmussen <morten.rasmussen@....com>
> Cc: Peter Zijlstra <peterz@...radead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@...aro.org>
>
> squash! sched/fair: Move select_task_rq_fair slow-path into its own function
> ---
> kernel/sched/fair.c | 83 +++++++++++++++++++++++++++++++----------------------
> 1 file changed, 48 insertions(+), 35 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index c95880e216f6..f6e277c65235 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5509,10 +5509,10 @@ find_idlest_group(struct sched_domain *sd, struct task_struct *p,
> }
>
> /*
> - * find_idlest_cpu - find the idlest cpu among the cpus in group.
> + * find_idlest_group_cpu - find the idlest cpu among the cpus in group.
> */
> static int
> -find_idlest_cpu(struct sched_group *group, struct task_struct *p, int this_cpu)
> +find_idlest_group_cpu(struct sched_group *group, struct task_struct *p, int this_cpu)
> {
> unsigned long load, min_load = ULONG_MAX;
> unsigned int min_exit_latency = UINT_MAX;
> @@ -5561,6 +5561,50 @@ find_idlest_cpu(struct sched_group *group, struct task_struct *p, int this_cpu)
> return shallowest_idle_cpu != -1 ? shallowest_idle_cpu : least_loaded_cpu;
> }
>
> +static inline int find_idlest_cpu(struct sched_domain *sd, struct task_struct *p,
> + int cpu, int prev_cpu, int sd_flag)
> +{
> + int new_cpu = prev_cpu;
> +
> + while (sd) {
> + struct sched_group *group;
> + struct sched_domain *tmp;
> + int weight;
> +
> + if (!(sd->flags & sd_flag)) {
> + sd = sd->child;
> + continue;
> + }
> +
> + group = find_idlest_group(sd, p, cpu, sd_flag);
> + if (!group) {
> + sd = sd->child;
> + continue;
> + }
> +
> + new_cpu = find_idlest_group_cpu(group, p, cpu);
> + if (new_cpu == -1 || new_cpu == cpu) {
> + /* Now try balancing at a lower domain level of cpu */
> + sd = sd->child;
> + continue;
> + }
> +
> + /* Now try balancing at a lower domain level of new_cpu */
> + cpu = new_cpu;
> + weight = sd->span_weight;
> + sd = NULL;
> + for_each_domain(cpu, tmp) {
> + if (weight <= tmp->span_weight)
> + break;
> + if (tmp->flags & sd_flag)
> + sd = tmp;
> + }
> + /* while loop will break here if sd == NULL */
> + }
> +
> + return new_cpu;
> +}
> +
> #ifdef CONFIG_SCHED_SMT
>
> static inline void set_idle_cores(int cpu, int val)
> @@ -5918,39 +5962,8 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_f
> if (sd_flag & SD_BALANCE_WAKE) /* XXX always ? */
> new_cpu = select_idle_sibling(p, prev_cpu, new_cpu);
>
> - } else while (sd) {
> - struct sched_group *group;
> - int weight;
> -
> - if (!(sd->flags & sd_flag)) {
> - sd = sd->child;
> - continue;
> - }
> -
> - group = find_idlest_group(sd, p, cpu, sd_flag);
> - if (!group) {
> - sd = sd->child;
> - continue;
> - }
> -
> - new_cpu = find_idlest_cpu(group, p, cpu);
> - if (new_cpu == -1 || new_cpu == cpu) {
> - /* Now try balancing at a lower domain level of cpu */
> - sd = sd->child;
> - continue;
> - }
> -
> - /* Now try balancing at a lower domain level of new_cpu */
> - cpu = new_cpu;
> - weight = sd->span_weight;
> - sd = NULL;
> - for_each_domain(cpu, tmp) {
> - if (weight <= tmp->span_weight)
> - break;
> - if (tmp->flags & sd_flag)
> - sd = tmp;
> - }
> - /* while loop will break here if sd == NULL */
> + } else {
> + new_cpu = find_idlest_cpu(sd, p, cpu, prev_cpu, sd_flag);
> }
> rcu_read_unlock();
>
> --
> 2.14.1
>
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