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Subject[tip:sched/urgent] sched/fair: Restructure wake_affine*() to return a CPU id
Commit-ID:  3b76c4a33959ca98a573cd9c94c8690d123912ca
Gitweb: https://git.kernel.org/tip/3b76c4a33959ca98a573cd9c94c8690d123912ca
Author: Mel Gorman <mgorman@techsingularity.net>
AuthorDate: Tue, 30 Jan 2018 10:45:53 +0000
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 6 Feb 2018 10:20:35 +0100

sched/fair: Restructure wake_affine*() to return a CPU id

This is a preparation patch that has wake_affine*() return a CPU ID instead of
a boolean. The intent is to allow the wake_affine() helpers to be avoided
if a decision is already made. This patch has no functional change.

Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20180130104555.4125-3-mgorman@techsingularity.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
kernel/sched/fair.c | 35 +++++++++++++++++------------------
1 file changed, 17 insertions(+), 18 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 0a551dfe..4c400d7 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5692,7 +5692,7 @@ static int wake_wide(struct task_struct *p)
* scheduling latency of the CPUs. This seems to work
* for the overloaded case.
*/
-static bool
+static int
wake_affine_idle(int this_cpu, int prev_cpu, int sync)
{
/*
@@ -5702,15 +5702,15 @@ wake_affine_idle(int this_cpu, int prev_cpu, int sync)
* node depending on the IO topology or IRQ affinity settings.
*/
if (idle_cpu(this_cpu) && cpus_share_cache(this_cpu, prev_cpu))
- return true;
+ return this_cpu;

if (sync && cpu_rq(this_cpu)->nr_running == 1)
- return true;
+ return this_cpu;

- return false;
+ return nr_cpumask_bits;
}

-static bool
+static int
wake_affine_weight(struct sched_domain *sd, struct task_struct *p,
int this_cpu, int prev_cpu, int sync)
{
@@ -5724,7 +5724,7 @@ wake_affine_weight(struct sched_domain *sd, struct task_struct *p,
unsigned long current_load = task_h_load(current);

if (current_load > this_eff_load)
- return true;
+ return this_cpu;

this_eff_load -= current_load;
}
@@ -5741,28 +5741,28 @@ wake_affine_weight(struct sched_domain *sd, struct task_struct *p,
prev_eff_load *= 100 + (sd->imbalance_pct - 100) / 2;
prev_eff_load *= capacity_of(this_cpu);

- return this_eff_load <= prev_eff_load;
+ return this_eff_load <= prev_eff_load ? this_cpu : nr_cpumask_bits;
}

static int wake_affine(struct sched_domain *sd, struct task_struct *p,
int prev_cpu, int sync)
{
int this_cpu = smp_processor_id();
- bool affine = false;
+ int target = nr_cpumask_bits;

if (sched_feat(WA_IDLE))
- affine = wake_affine_idle(this_cpu, prev_cpu, sync);
+ target = wake_affine_idle(this_cpu, prev_cpu, sync);

- if (sched_feat(WA_WEIGHT) && !affine)
- affine = wake_affine_weight(sd, p, this_cpu, prev_cpu, sync);
+ if (sched_feat(WA_WEIGHT) && target == nr_cpumask_bits)
+ target = wake_affine_weight(sd, p, this_cpu, prev_cpu, sync);

schedstat_inc(p->se.statistics.nr_wakeups_affine_attempts);
- if (affine) {
- schedstat_inc(sd->ttwu_move_affine);
- schedstat_inc(p->se.statistics.nr_wakeups_affine);
- }
+ if (target == nr_cpumask_bits)
+ return prev_cpu;

- return affine;
+ schedstat_inc(sd->ttwu_move_affine);
+ schedstat_inc(p->se.statistics.nr_wakeups_affine);
+ return target;
}

static inline unsigned long task_util(struct task_struct *p);
@@ -6355,8 +6355,7 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_f
if (cpu == prev_cpu)
goto pick_cpu;

- if (wake_affine(affine_sd, p, prev_cpu, sync))
- new_cpu = cpu;
+ new_cpu = wake_affine(affine_sd, p, prev_cpu, sync);
}

if (sd && !(sd_flag & SD_BALANCE_FORK)) {
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