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From 4e4846aafb09473f1ca69fa061e72437b55f78c7 Mon Sep 17 00:00:00 2001
From: Vincent Guittot <vincent.guittot@linaro.org>
Date: Thu, 8 Dec 2016 17:56:53 +0100
Subject: [PATCH 80/92] sched/core: Fix find_idlest_group() for fork
During fork, the utilization of a task is init once the rq has been
selected because the current utilization level of the rq is used to
set the utilization of the fork task. As the task's utilization is
still 0 at this step of the fork sequence, it doesn't make sense to
look for some spare capacity that can fit the task's utilization.
Furthermore, I can see perf regressions for the test:
hackbench -P -g 1
because the least loaded policy is always bypassed and tasks are not
spread during fork.
With this patch and the fix below, we are back to same performances as
for v4.8. The fix below is only a temporary one used for the test
until a smarter solution is found because we can't simply remove the
test which is useful for others benchmarks
| @@ -5708,13 +5708,6 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
|
| avg_cost = this_sd->avg_scan_cost;
|
| - /*
| - * Due to large variance we need a large fuzz factor; hackbench in
| - * particularly is sensitive here.
| - */
| - if ((avg_idle / 512) < avg_cost)
| - return -1;
| -
| time = local_clock();
|
| for_each_cpu_wrap(cpu, sched_domain_span(sd), target, wrap) {
Tested-by: Matt Fleming <matt@codeblueprint.co.uk>
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Matt Fleming <matt@codeblueprint.co.uk>
Acked-by: Morten Rasmussen <morten.rasmussen@arm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dietmar.eggemann@arm.com
Cc: kernellwp@gmail.com
Cc: umgwanakikbuti@gmail.com
Cc: yuyang.du@intel.comc
Link: http://lkml.kernel.org/r/1481216215-24651-2-git-send-email-vincent.guittot@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
(cherry picked from commit f2e4ac502860c2adcc5ce56e0064fc4bcab90af4)
Signed-off-by: Gaku Inami <gaku.inami.xw@bp.renesas.com>
---
kernel/sched/fair.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 489f6d3..fea3ca8 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5809,13 +5809,21 @@ static unsigned long capacity_spare_wake(int cpu, struct task_struct *p)
* utilized systems if we require spare_capacity > task_util(p),
* so we allow for some task stuffing by using
* spare_capacity > task_util(p)/2.
+ *
+ * Spare capacity can't be used for fork because the utilization has
+ * not been set yet, we must first select a rq to compute the initial
+ * utilization.
*/
+ if (sd_flag & SD_BALANCE_FORK)
+ goto skip_spare;
+
if (this_spare > task_util(p) / 2 &&
imbalance*this_spare > 100*most_spare)
return NULL;
else if (most_spare > task_util(p) / 2)
return most_spare_sg;
+skip_spare:
if (!idlest || 100*this_load < imbalance*min_load)
return NULL;
return idlest;
--
1.9.1
|
