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Commit 3273163c authored by Morten Rasmussen's avatar Morten Rasmussen Committed by Ingo Molnar
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sched/fair: Let asymmetric CPU configurations balance at wake-up 



Currently, SD_WAKE_AFFINE always takes priority over wakeup balancing if
SD_BALANCE_WAKE is set on the sched_domains. For asymmetric
configurations SD_WAKE_AFFINE is only desirable if the waking task's
compute demand (utilization) is suitable for the waking CPU and the
previous CPU, and all CPUs within their respective
SD_SHARE_PKG_RESOURCES domains (sd_llc). If not, let wakeup balancing
take over (find_idlest_{group, cpu}()).

This patch makes affine wake-ups conditional on whether both the waker
CPU and the previous CPU has sufficient capacity for the waking task,
or not, assuming that the CPU capacities within an SD_SHARE_PKG_RESOURCES
domain (sd_llc) are homogeneous.

Signed-off-by: default avatarMorten Rasmussen <morten.rasmussen@arm.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: default avatarVincent Guittot <vincent.guittot@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dietmar.eggemann@arm.com
Cc: freedom.tan@mediatek.com
Cc: keita.kobayashi.ym@renesas.com
Cc: mgalbraith@suse.de
Cc: sgurrappadi@nvidia.com
Cc: yuyang.du@intel.com
Link: http://lkml.kernel.org/r/1469453670-2660-10-git-send-email-morten.rasmussen@arm.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent cd92bfd3

kernel/sched/fair.c

+34 −1
Original line number Diff line number Diff line
@@ -114,6 +114,12 @@ unsigned int __read_mostly sysctl_sched_shares_window = 10000000UL; 
unsigned int sysctl_sched_cfs_bandwidth_slice = 5000UL;

#endif



/*

 * The margin used when comparing utilization with CPU capacity:

 * util * 1024 < capacity * margin

 */

unsigned int capacity_margin = 1280; /* ~20% */



static inline void update_load_add(struct load_weight *lw, unsigned long inc)

{

	lw->weight += inc;
@@ -5376,6 +5382,32 @@ static int cpu_util(int cpu) 
	return (util >= capacity) ? capacity : util;

}



static inline int task_util(struct task_struct *p)

{

	return p->se.avg.util_avg;

}



/*

 * Disable WAKE_AFFINE in the case where task @p doesn't fit in the

 * capacity of either the waking CPU @cpu or the previous CPU @prev_cpu.

 *

 * In that case WAKE_AFFINE doesn't make sense and we'll let

 * BALANCE_WAKE sort things out.

 */

static int wake_cap(struct task_struct *p, int cpu, int prev_cpu)

{

	long min_cap, max_cap;



	min_cap = min(capacity_orig_of(prev_cpu), capacity_orig_of(cpu));

	max_cap = cpu_rq(cpu)->rd->max_cpu_capacity;



	/* Minimum capacity is close to max, no need to abort wake_affine */

	if (max_cap - min_cap < max_cap >> 3)

		return 0;



	return min_cap * 1024 < task_util(p) * capacity_margin;

}



/*

 * select_task_rq_fair: Select target runqueue for the waking task in domains

 * that have the 'sd_flag' flag set. In practice, this is SD_BALANCE_WAKE,
@@ -5399,7 +5431,8 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_f 


	if (sd_flag & SD_BALANCE_WAKE) {

		record_wakee(p);

		want_affine = !wake_wide(p) && cpumask_test_cpu(cpu, tsk_cpus_allowed(p));

		want_affine = !wake_wide(p) && !wake_cap(p, cpu, prev_cpu)

			      && cpumask_test_cpu(cpu, tsk_cpus_allowed(p));

	}



	rcu_read_lock();