52 lines
1.8 KiB
Diff
52 lines
1.8 KiB
Diff
From f87f3c003eb4ad513e6732dfaa76f442b8aec9ba Mon Sep 17 00:00:00 2001
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From: Nicholas Mc Guire <der.herr@hofr.at>
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Date: Mon, 24 Mar 2014 13:18:48 +0100
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Subject: [PATCH] sched: dont calculate hweight in update_migrate_disable()
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Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.0/patches-4.0.5-rt3.tar.xz
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Proposal for a minor optimization in update_migrate_disable - its only a few
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instructions saved but those are in the hot path of locks so it might be worth
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it
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When being scheduled out while migrate_disable > 0 and migrate_disabled_updated
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is not yet set we end up here (kernel/sched/core.c):
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static inline void update_migrate_disable(struct task_struct *p)
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{
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...
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mask = tsk_cpus_allowed(p);
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if (p->sched_class->set_cpus_allowed)
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p->sched_class->set_cpus_allowed(p, mask);
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p->nr_cpus_allowed = cpumask_weight(mask);
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as we only can get here if migrate_disable > 0 there is no need to calculate
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the cpumask_weight(mask) as tsk_cpus_allowed in that case will return
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cpumask_of(task_cpu(p)) which only can have a hamming weight of 1 anyway.
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So we can simply do:
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p->nr_cpus_allowed = 1;
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without changing the behavior.
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Reviewed-by: Steven Rostedt <rostedt@goodmis.org>
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Signed-off-by: Nicholas Mc Guire <der.herr@hofr.at>
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Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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---
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kernel/sched/core.c | 3 ++-
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1 file changed, 2 insertions(+), 1 deletion(-)
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--- a/kernel/sched/core.c
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+++ b/kernel/sched/core.c
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@@ -2732,7 +2732,8 @@ static inline void update_migrate_disabl
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if (p->sched_class->set_cpus_allowed)
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p->sched_class->set_cpus_allowed(p, mask);
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- p->nr_cpus_allowed = cpumask_weight(mask);
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+ /* mask==cpumask_of(task_cpu(p)) which has a cpumask_weight==1 */
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+ p->nr_cpus_allowed = 1;
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/* Let migrate_enable know to fix things back up */
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p->migrate_disable |= MIGRATE_DISABLE_SET_AFFIN;
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