From: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
To: Ingo Molnar <mingo@kernel.org>, Peter Zijlstra <peterz@infradead.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
Mel Gorman <mgorman@techsingularity.net>,
Rik van Riel <riel@surriel.com>,
Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
Thomas Gleixner <tglx@linutronix.de>,
Valentin Schneider <valentin.schneider@arm.com>,
Vincent Guittot <vincent.guittot@linaro.org>
Subject: [PATCH v2] sched/fair: Optimize select_idle_core
Date: Fri, 6 Dec 2019 22:54:22 +0530 [thread overview]
Message-ID: <20191206172422.6578-1-srikar@linux.vnet.ibm.com> (raw)
Currently we loop through all threads of a core to evaluate if the core is
idle or not. This is unnecessary. If a thread of a core is not idle, skip
evaluating other threads of a core. Also while clearing the cpumask, bits
of all CPUs of a core can be cleared in one-shot.
Collecting ticks on a Power 9 SMT 8 system around select_idle_core
while running schbench shows us
(units are in ticks, hence lesser is better)
Without patch
N Min Max Median Avg Stddev
x 130 151 1083 284 322.72308 144.41494
With patch
N Min Max Median Avg Stddev Improvement
x 164 88 610 201 225.79268 106.78943 30.03%
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
---
Changelog v1->v2:
Updated patch description with measurements made from a debug patch.
kernel/sched/fair.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 69a81a5709ff..b9d628128cfc 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5872,10 +5872,12 @@ static int select_idle_core(struct task_struct *p, struct sched_domain *sd, int
bool idle = true;
for_each_cpu(cpu, cpu_smt_mask(core)) {
- __cpumask_clear_cpu(cpu, cpus);
- if (!available_idle_cpu(cpu))
+ if (!available_idle_cpu(cpu)) {
idle = false;
+ break;
+ }
}
+ cpumask_andnot(cpus, cpus, cpu_smt_mask(core));
if (idle)
return core;
--
2.18.1
next reply other threads:[~2019-12-06 17:24 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-06 17:24 Srikar Dronamraju [this message]
2020-01-22 13:55 ` [PATCH v2] sched/fair: Optimize select_idle_core Mel Gorman
2020-01-22 14:22 ` Valentin Schneider
2020-01-24 13:32 ` Srikar Dronamraju
2020-01-29 11:32 ` [tip: sched/core] sched/fair: Optimize select_idle_core() tip-bot2 for Srikar Dronamraju
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