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sched/fair: Let asymmetric CPU configurations balance at wake-up

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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: Morten Rasmussen <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Acked-by: Vincent Guittot <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Mike Galbraith <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
This commit is contained in:
Morten Rasmussen 2016-07-25 14:34:26 +01:00 • committed by Ingo Molnar
commit 3273163c67
1 changed files with 34 additions and 1 deletions
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35
kernel/sched/fair.c
View file

@ -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();