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sched/fair: Spread out tasks evenly when not overloaded

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When there is only one CPU per group, using the idle CPUs to evenly spread
tasks doesn't make sense and nr_running is a better metrics.

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Ben Segall <bsegall@google.com>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Morten.Rasmussen@arm.com
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: hdanton@sina.com
Cc: parth@linux.ibm.com
Cc: pauld@redhat.com
Cc: quentin.perret@arm.com
Cc: riel@surriel.com
Cc: srikar@linux.vnet.ibm.com
Cc: valentin.schneider@arm.com
Link: https://lkml.kernel.org/r/1571405198-27570-8-git-send-email-vincent.guittot@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Vincent Guittot 2019-10-18 15:26:34 +02:00 committed by Ingo Molnar
parent b0fb1eb4f0
commit 2ab4092fc8
1 changed files with 28 additions and 12 deletions
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40
kernel/sched/fair.c
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@ -8591,18 +8591,34 @@ static struct sched_group *find_busiest_group(struct lb_env *env)
busiest->sum_nr_running > local->sum_nr_running + 1)
goto force_balance;
if (busiest->group_type != group_overloaded &&
(env->idle == CPU_NOT_IDLE ||
local->idle_cpus <= (busiest->idle_cpus + 1)))
/*
* If the busiest group is not overloaded
* and there is no imbalance between this and busiest group
* wrt. idle CPUs, it is balanced. The imbalance
* becomes significant if the diff is greater than 1 otherwise
* we might end up just moving the imbalance to another
* group.
*/
goto out_balanced;
if (busiest->group_type != group_overloaded) {
if (env->idle == CPU_NOT_IDLE)
/*
* If the busiest group is not overloaded (and as a
* result the local one too) but this CPU is already
* busy, let another idle CPU try to pull task.
*/
goto out_balanced;
if (busiest->group_weight > 1 &&
local->idle_cpus <= (busiest->idle_cpus + 1))
/*
* If the busiest group is not overloaded
* and there is no imbalance between this and busiest
* group wrt idle CPUs, it is balanced. The imbalance
* becomes significant if the diff is greater than 1
* otherwise we might end up to just move the imbalance
* on another group. Of course this applies only if
* there is more than 1 CPU per group.
*/
goto out_balanced;
if (busiest->sum_h_nr_running == 1)
/*
* busiest doesn't have any tasks waiting to run
*/
goto out_balanced;
}
force_balance:
/* Looks like there is an imbalance. Compute it */