Task migration happens when target just a bit less then source cpu load.
To reduce such situation happens, aggravate the target cpu load with
sd->imbalance_pct/100.
This patch removes the hackbench thread regression on Daniel's
Intel Core2 server.
a5d6e63 +patch1~3 +patch1~4
hackbench -T -s 4096 -l 1000 -g 10 -f 40
27.914" 38.694" 28.587"
28.390" 38.341" 29.513"
28.048" 38.626" 28.706"
Signed-off-by: Alex Shi <alex....@linaro.org>
---
kernel/sched/fair.c | 18 ++++++++++++------
1 file changed, 12 insertions(+), 6 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index bccdd89..c49b7ba 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -978,7 +978,7 @@ static inline unsigned long group_weight(struct task_struct
*p, int nid)
static unsigned long weighted_cpuload(const int cpu);
static unsigned long source_load(int cpu);
-static unsigned long target_load(int cpu);
+static unsigned long target_load(int cpu, int imbalance_pct);
static unsigned long power_of(int cpu);
static long effective_load(struct task_group *tg, int cpu, long wl, long wg);
@@ -3809,11 +3809,17 @@ static unsigned long source_load(int cpu)
* Return a high guess at the load of a migration-target cpu weighted
* according to the scheduling class and "nice" value.
*/
-static unsigned long target_load(int cpu)
+static unsigned long target_load(int cpu, int imbalance_pct)
{
struct rq *rq = cpu_rq(cpu);
unsigned long total = weighted_cpuload(cpu);
+ /*
+ * without cpu_load decay, in most of time cpu_load is same as total
+ * so we need to make target a bit heavier to reduce task migration
+ */
+ total = total * imbalance_pct / 100;
+
if (!sched_feat(LB_BIAS))
return total;
@@ -4033,7 +4039,7 @@ static int wake_affine(struct sched_domain *sd, struct
task_struct *p, int sync)
this_cpu = smp_processor_id();
prev_cpu = task_cpu(p);
load = source_load(prev_cpu);
- this_load = target_load(this_cpu);
+ this_load = target_load(this_cpu, 100);
/*
* If sync wakeup then subtract the (maximum possible)
@@ -4089,7 +4095,7 @@ static int wake_affine(struct sched_domain *sd, struct
task_struct *p, int sync)
if (balanced ||
(this_load <= load &&
- this_load + target_load(prev_cpu) <= tl_per_task)) {
+ this_load + target_load(prev_cpu, 100) <= tl_per_task)) {
/*
* This domain has SD_WAKE_AFFINE and
* p is cache cold in this domain, and
@@ -4135,7 +4141,7 @@ find_idlest_group(struct sched_domain *sd, struct
task_struct *p, int this_cpu)
if (local_group)
load = source_load(i);
else
- load = target_load(i);
+ load = target_load(i, sd->imbalance_pct);
avg_load += load;
}
@@ -5478,7 +5484,7 @@ static inline void update_sg_lb_stats(struct lb_env *env,
/* Bias balancing toward cpus of our domain */
if (local_group)
- load = target_load(i);
+ load = target_load(i, env->sd->imbalance_pct);
else
load = source_load(i);
--
1.8.1.2
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
