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Commit da84d961 authored by Ingo Molnar's avatar Ingo Molnar
Browse files

sched: reintroduce cache-hot affinity



reintroduce a simplified version of cache-hot/cold scheduling
affinity. This improves performance with certain SMP workloads,
such as sysbench.

Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent e5f32a38
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+1 −0
Original line number Diff line number Diff line
@@ -1415,6 +1415,7 @@ extern unsigned int sysctl_sched_wakeup_granularity;
extern unsigned int sysctl_sched_batch_wakeup_granularity;
extern unsigned int sysctl_sched_child_runs_first;
extern unsigned int sysctl_sched_features;
extern unsigned int sysctl_sched_migration_cost;
#endif

extern unsigned int sysctl_sched_compat_yield;
+27 −0
Original line number Diff line number Diff line
@@ -2118,6 +2118,17 @@ static void pull_task(struct rq *src_rq, struct task_struct *p,
	check_preempt_curr(this_rq, p);
}

/*
 * Is this task likely cache-hot:
 */
static inline int
task_hot(struct task_struct *p, unsigned long long now, struct sched_domain *sd)
{
	s64 delta = now - p->se.exec_start;

	return delta < (long long)sysctl_sched_migration_cost;
}

/*
 * can_migrate_task - may task p from runqueue rq be migrated to this_cpu?
 */
@@ -2139,6 +2150,22 @@ int can_migrate_task(struct task_struct *p, struct rq *rq, int this_cpu,
	if (task_running(rq, p))
		return 0;

	/*
	 * Aggressive migration if:
	 * 1) task is cache cold, or
	 * 2) too many balance attempts have failed.
	 */

	if (sd->nr_balance_failed > sd->cache_nice_tries) {
#ifdef CONFIG_SCHEDSTATS
		if (task_hot(p, rq->clock, sd))
			schedstat_inc(sd, lb_hot_gained[idle]);
#endif
		return 1;
	}

	if (task_hot(p, rq->clock, sd))
		return 0;
	return 1;
}

+2 −0
Original line number Diff line number Diff line
@@ -74,6 +74,8 @@ const_debug unsigned int sysctl_sched_batch_wakeup_granularity = 10000000UL;
 */
const_debug unsigned int sysctl_sched_wakeup_granularity = 10000000UL;

const_debug unsigned int sysctl_sched_migration_cost = 500000UL;

/**************************************************************
 * CFS operations on generic schedulable entities:
 */
+8 −0
Original line number Diff line number Diff line
@@ -277,6 +277,14 @@ static ctl_table kern_table[] = {
		.mode		= 0644,
		.proc_handler	= &proc_dointvec,
	},
	{
		.ctl_name	= CTL_UNNUMBERED,
		.procname	= "sched_migration_cost",
		.data		= &sysctl_sched_migration_cost,
		.maxlen		= sizeof(unsigned int),
		.mode		= 0644,
		.proc_handler	= &proc_dointvec,
	},
#endif
	{
		.ctl_name	= CTL_UNNUMBERED,