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Commit 2398f2c6 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

sched: update shares on wakeup 



We found that the affine wakeup code needs rather accurate load figures
to be effective. The trouble is that updating the load figures is fairly
expensive with group scheduling. Therefore ratelimit the updating.

Signed-off-by: default avatarPeter Zijlstra <peterz@infradead.org>
Cc: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Cc: Mike Galbraith <efault@gmx.de>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent cd80917e

include/linux/sched.h

+3 −0
Original line number Diff line number Diff line
@@ -783,6 +783,8 @@ struct sched_domain { 
	unsigned int balance_interval;	/* initialise to 1. units in ms. */

	unsigned int nr_balance_failed; /* initialise to 0 */



	u64 last_update;



#ifdef CONFIG_SCHEDSTATS

	/* load_balance() stats */

	unsigned int lb_count[CPU_MAX_IDLE_TYPES];
@@ -1605,6 +1607,7 @@ extern unsigned int sysctl_sched_child_runs_first; 
extern unsigned int sysctl_sched_features;

extern unsigned int sysctl_sched_migration_cost;

extern unsigned int sysctl_sched_nr_migrate;

extern unsigned int sysctl_sched_shares_ratelimit;



int sched_nr_latency_handler(struct ctl_table *table, int write,

		struct file *file, void __user *buffer, size_t *length,

kernel/sched.c

+29 −1
Original line number Diff line number Diff line
@@ -777,6 +777,12 @@ late_initcall(sched_init_debug); 
 */

const_debug unsigned int sysctl_sched_nr_migrate = 32;



/*

 * ratelimit for updating the group shares.

 * default: 0.5ms

 */

const_debug unsigned int sysctl_sched_shares_ratelimit = 500000;



/*

 * period over which we measure -rt task cpu usage in us.

 * default: 1s
@@ -1590,8 +1596,14 @@ tg_nop(struct task_group *tg, int cpu, struct sched_domain *sd) 


static void update_shares(struct sched_domain *sd)

{

	u64 now = cpu_clock(raw_smp_processor_id());

	s64 elapsed = now - sd->last_update;



	if (elapsed >= (s64)(u64)sysctl_sched_shares_ratelimit) {

		sd->last_update = now;

		walk_tg_tree(tg_nop, tg_shares_up, 0, sd);

	}

}



static void update_shares_locked(struct rq *rq, struct sched_domain *sd)

{
@@ -2199,6 +2211,22 @@ static int try_to_wake_up(struct task_struct *p, unsigned int state, int sync) 
	if (!sched_feat(SYNC_WAKEUPS))

		sync = 0;



#ifdef CONFIG_SMP

	if (sched_feat(LB_WAKEUP_UPDATE)) {

		struct sched_domain *sd;



		this_cpu = raw_smp_processor_id();

		cpu = task_cpu(p);



		for_each_domain(this_cpu, sd) {

			if (cpu_isset(cpu, sd->span)) {

				update_shares(sd);

				break;

			}

		}

	}

#endif



	smp_wmb();

	rq = task_rq_lock(p, &flags);

	old_state = p->state;

kernel/sched_features.h

+2 −1
Original line number Diff line number Diff line
@@ -9,3 +9,4 @@ SCHED_FEAT(HRTICK, 1) 
SCHED_FEAT(DOUBLE_TICK, 0)

SCHED_FEAT(ASYM_GRAN, 1)

SCHED_FEAT(LB_BIAS, 0)

SCHED_FEAT(LB_WAKEUP_UPDATE, 1)

kernel/sysctl.c

+8 −0
Original line number Diff line number Diff line
@@ -264,6 +264,14 @@ static struct ctl_table kern_table[] = { 
		.extra1		= &min_wakeup_granularity_ns,

		.extra2		= &max_wakeup_granularity_ns,

	},

	{

		.ctl_name	= CTL_UNNUMBERED,

		.procname	= "sched_shares_ratelimit",

		.data		= &sysctl_sched_shares_ratelimit,

		.maxlen		= sizeof(unsigned int),

		.mode		= 0644,

		.proc_handler	= &proc_dointvec,

	},

	{

		.ctl_name	= CTL_UNNUMBERED,

		.procname	= "sched_child_runs_first",