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Subject[tip:sched/core] sched/fair: Rearrange select_task_rq_fair() to optimize it
Commit-ID:  f1d88b4468188ddcd2620b8d612068faf6662a62
Gitweb: https://git.kernel.org/tip/f1d88b4468188ddcd2620b8d612068faf6662a62
Author: Viresh Kumar <viresh.kumar@linaro.org>
AuthorDate: Thu, 26 Apr 2018 16:00:50 +0530
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Fri, 4 May 2018 10:00:07 +0200

sched/fair: Rearrange select_task_rq_fair() to optimize it

Rearrange select_task_rq_fair() a bit to avoid executing some
conditional statements in few specific code-paths. That gets rid of the
goto as well.

This shouldn't result in any functional changes.

Tested-by: Rohit Jain <rohit.k.jain@oracle.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Link: http://lkml.kernel.org/r/20831b8d237bf3a20e4e328286f678b425ff04c9.1524738578.git.viresh.kumar@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
kernel/sched/fair.c | 37 ++++++++++++++++---------------------
1 file changed, 16 insertions(+), 21 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index e3002e5ada31..4b346f358005 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6613,7 +6613,7 @@ static int wake_cap(struct task_struct *p, int cpu, int prev_cpu)
static int
select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_flags)
{
- struct sched_domain *tmp, *affine_sd = NULL, *sd = NULL;
+ struct sched_domain *tmp, *sd = NULL;
int cpu = smp_processor_id();
int new_cpu = prev_cpu;
int want_affine = 0;
@@ -6636,7 +6636,10 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_f
*/
if (want_affine && (tmp->flags & SD_WAKE_AFFINE) &&
cpumask_test_cpu(prev_cpu, sched_domain_span(tmp))) {
- affine_sd = tmp;
+ if (cpu != prev_cpu)
+ new_cpu = wake_affine(tmp, p, cpu, prev_cpu, sync);
+
+ sd = NULL; /* Prefer wake_affine over balance flags */
break;
}

@@ -6646,33 +6649,25 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_f
break;
}

- if (affine_sd) {
- sd = NULL; /* Prefer wake_affine over balance flags */
- if (cpu == prev_cpu)
- goto pick_cpu;
-
- new_cpu = wake_affine(affine_sd, p, cpu, prev_cpu, sync);
- }
+ if (unlikely(sd)) {
+ /* Slow path */

- if (sd && !(sd_flag & SD_BALANCE_FORK)) {
/*
* We're going to need the task's util for capacity_spare_wake
* in find_idlest_group. Sync it up to prev_cpu's
* last_update_time.
*/
- sync_entity_load_avg(&p->se);
- }
-
- if (!sd) {
-pick_cpu:
- if (sd_flag & SD_BALANCE_WAKE) { /* XXX always ? */
- new_cpu = select_idle_sibling(p, prev_cpu, new_cpu);
+ if (!(sd_flag & SD_BALANCE_FORK))
+ sync_entity_load_avg(&p->se);

- if (want_affine)
- current->recent_used_cpu = cpu;
- }
- } else {
new_cpu = find_idlest_cpu(sd, p, cpu, prev_cpu, sd_flag);
+ } else if (sd_flag & SD_BALANCE_WAKE) { /* XXX always ? */
+ /* Fast path */
+
+ new_cpu = select_idle_sibling(p, prev_cpu, new_cpu);
+
+ if (want_affine)
+ current->recent_used_cpu = cpu;
}
rcu_read_unlock();

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