Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1449487

[PATCH v3 09/13] sched/fair: Let asymmetric cpu configurations balance at wake-up

Show all headers | View raw

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 prev_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.

cc: Ingo Molnar <mingo@redhat.com>
cc: Peter Zijlstra <peterz@infradead.org>

Acked-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
---
 kernel/sched/fair.c | 28 +++++++++++++++++++++++++++-
 1 file changed, 27 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index c1c0aa8b300b..9e217eff3daf 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -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;
@@ -5366,6 +5372,25 @@ 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;
+}
+
+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,
@@ -5389,7 +5414,8 @@ 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();
-- 
1.9.1

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

[PATCH v3 00/13] sched: Clean-ups and asymmetric cpu capacity support Morten Rasmussen <morten.rasmussen@arm.com> - 2016-07-25 15:40 +0200
  [PATCH v3 09/13] sched/fair: Let asymmetric cpu configurations balance at wake-up Morten Rasmussen <morten.rasmussen@arm.com> - 2016-07-25 15:40 +0200
  [PATCH v3 13/13] sched/fair: Avoid pulling tasks from non-overloaded higher capacity groups Morten Rasmussen <morten.rasmussen@arm.com> - 2016-07-25 15:40 +0200
  [PATCH v3 06/13] sched/core: Pass child domain into sd_init Morten Rasmussen <morten.rasmussen@arm.com> - 2016-07-25 15:40 +0200
  [PATCH v3 05/13] sched: Introduce SD_ASYM_CPUCAPACITY sched_domain topology flag Morten Rasmussen <morten.rasmussen@arm.com> - 2016-07-25 15:40 +0200
  [PATCH v3 08/13] sched: Store maximum per-cpu capacity in root domain Morten Rasmussen <morten.rasmussen@arm.com> - 2016-07-25 15:40 +0200
  [PATCH v3 10/13] sched/fair: Compute task/cpu utilization at wake-up more correctly Morten Rasmussen <morten.rasmussen@arm.com> - 2016-07-25 15:40 +0200
  [PATCH v3 04/13] sched/core: Remove unnecessary null-pointer check Morten Rasmussen <morten.rasmussen@arm.com> - 2016-07-25 15:40 +0200
  [PATCH v3 03/13] sched/fair: Optimize find_idlest_cpu() when there is no choice Morten Rasmussen <morten.rasmussen@arm.com> - 2016-07-25 15:40 +0200

csiph-web