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SubjectRe: [sched] 73628fba4: +69% context switches
On 01/11/2014 06:19 PM, Fengguang Wu wrote:
> Alex,
>
> FYI, we find much increased interrupts and context switches introduced
> by commit 73628fba4 ("sched: unify imbalance bias for target group")
> in your noload branch:

Many thanks for the generous and quick testing! :)

few questions for the results and give a testing patch for try. it also push on github.

What's about the aim7 shell_rtns_1 and shared throughput?
>
> 7bea8c18805a5f1 73628fba451ae72221b155696
> --------------- -------------------------
> 14979 ~ 4% +1304.8% 210434 ~ 1% lkp-ne04/micro/aim7/shell_rtns_1
> 2748 ~ 5% +977.4% 29607 ~ 0% nhm-white/micro/aim7/shared
> 17727 +1254.1% 240041 TOTAL interrupts.RES

RES interrupt increased about 200,000, but vmstat's interrupt increased a little. guess the vmstat data is per seconds, right? If so, it is better give how long time the vmstat running.

The same problem on the time.involuntary_context_switches and vmstat cs.

According to involuntary CS definition in time, RES interrupt will cause involuntary CS. but here 29607 RES of aim7/shared cause 233218 time inv CS, does sth I missed or the data is incorrect?

>
> 7bea8c18805a5f1 73628fba451ae72221b155696
> --------------- -------------------------
> 3617 ~ 0% +69.2% 6118 ~ 0% lkp-ne04/micro/aim7/shell_rtns_1
> 3617 +69.2% 6118 TOTAL vmstat.system.in
>
> 7bea8c18805a5f1 73628fba451ae72221b155696
> --------------- -------------------------
> 132746 ~ 0% +69.0% 224346 ~ 1% lkp-ne04/micro/aim7/shell_rtns_1
> 220038 ~ 0% +6.0% 233218 ~ 0% nhm-white/micro/aim7/shared
> 352785 +29.7% 457564 TOTAL time.involuntary_context_switches
>
> 7bea8c18805a5f1 73628fba451ae72221b155696
> --------------- -------------------------
> 1424581 ~ 0% +8.6% 1546786 ~ 0% lkp-ne04/micro/aim7/shell_rtns_1
> 1424581 +8.6% 1546786 TOTAL time.voluntary_context_switches
>
> 7bea8c18805a5f1 73628fba451ae72221b155696
> --------------- -------------------------
> 20982 ~ 0% +12.5% 23599 ~ 0% lkp-ne04/micro/aim7/shell_rtns_1
> 6005 ~ 0% +4.2% 6256 ~ 0% nhm-white/micro/aim7/shared
> 26988 +10.6% 29856 TOTAL vmstat.system.cs
>
> vmstat.system.cs
>

commit c5a8778a132cfa882609fbccb4ee6542eac9866d
Author: Alex Shi <alex.shi@linaro.org>
Date: Mon Jan 13 13:54:30 2014 +0800

more bias towards local cpu group

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 2b216ad..046ca2c 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4008,7 +4008,6 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync)
struct task_group *tg;
unsigned long weight;
int balanced;
- int bias = 100 + (sd->imbalance_pct -100) / 2;

/*
* If we wake multiple tasks be careful to not bounce
@@ -4020,7 +4019,7 @@ 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, bias);
+ this_load = target_load(this_cpu, sd->imbalance_pct);

/*
* If sync wakeup then subtract the (maximum possible)
@@ -4055,7 +4054,7 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync)
this_eff_load *= this_load +
effective_load(tg, this_cpu, weight, weight);

- prev_eff_load = bias;
+ prev_eff_load = 100 + (sd->imbalance_pct - 100) / 2;
prev_eff_load *= power_of(this_cpu);
prev_eff_load *= load + effective_load(tg, prev_cpu, 0, weight);

@@ -4100,7 +4099,6 @@ find_idlest_group(struct sched_domain *sd, struct task_struct *p, int this_cpu)
{
struct sched_group *idlest = NULL, *group = sd->groups;
unsigned long min_load = ULONG_MAX, this_load = 0;
- int imbalance = 100 + (sd->imbalance_pct-100)/2;

do {
unsigned long load, avg_load;
@@ -4123,7 +4121,7 @@ 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, imbalance);
+ load = target_load(i, sd->imbalance_pct);

avg_load += load;
}
--
Thanks
Alex


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