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Date: Thu, 19 Dec 2013 21:34:08 +0800
From: Alex Shi <alex.shi@...aro.org>
To: Peter Zijlstra <peterz@...radead.org>,
Morten Rasmussen <morten.rasmussen@....com>
CC: "mingo@...hat.com" <mingo@...hat.com>,
"vincent.guittot@...aro.org" <vincent.guittot@...aro.org>,
"daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>,
"fweisbec@...il.com" <fweisbec@...il.com>,
"linux@....linux.org.uk" <linux@....linux.org.uk>,
"tony.luck@...el.com" <tony.luck@...el.com>,
"fenghua.yu@...el.com" <fenghua.yu@...el.com>,
"tglx@...utronix.de" <tglx@...utronix.de>,
"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
"arjan@...ux.intel.com" <arjan@...ux.intel.com>,
"pjt@...gle.com" <pjt@...gle.com>,
"fengguang.wu@...el.com" <fengguang.wu@...el.com>,
"james.hogan@...tec.com" <james.hogan@...tec.com>,
"jason.low2@...com" <jason.low2@...com>,
"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
"hanjun.guo@...aro.org" <hanjun.guo@...aro.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/4] sched: bias to target cpu load to reduce task moving
On 12/17/2013 11:38 PM, Peter Zijlstra wrote:
> On Tue, Dec 17, 2013 at 02:10:12PM +0000, Morten Rasmussen wrote:
>>> @@ -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);
>>
>> Don't you apply imbalance_pct twice here? Later on in
>> find_idlest_group() you have:
>>
>> if (!idlest || 100*this_load < imbalance*min_load)
>> return NULL;
>>
>> where min_load comes from target_load().
>
> Yes! exactly! this doesn't make any sense.
Thanks a lot for review and comments!
I changed the patch to following shape. and push it under Fengguang's testing
system monitor. Any testing are appreciated!
BTW, Seems lots of changes in scheduler come from kinds of scenarios/benchmarks
experience. But I still like to take any theoretical comments/suggestions.
--
Thanks
Alex
===
>From 5cd67d975001edafe2ee820e0be5d86881a23bd6 Mon Sep 17 00:00:00 2001
From: Alex Shi <alex.shi@...aro.org>
Date: Sat, 23 Nov 2013 23:18:09 +0800
Subject: [PATCH 4/4] sched: bias to target cpu load to reduce task moving
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 in wake_affine.
In find_idlest/busiest_group, change the aggravate to local cpu only
from old group aggravation.
on my pandaboard ES.
latest kernel 527d1511310a89 + whole patchset
hackbench -T -g 10 -f 40
23.25" 21.99"
23.16" 21.20"
24.24" 21.89"
hackbench -p -g 10 -f 40
26.52" 21.46"
23.89" 22.96"
25.65" 22.73"
hackbench -P -g 10 -f 40
20.14" 19.72"
19.96" 19.10"
21.76" 20.03"
Signed-off-by: Alex Shi <alex.shi@...aro.org>
---
kernel/sched/fair.c | 35 ++++++++++++++++-------------------
1 file changed, 16 insertions(+), 19 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index bccdd89..3623ba4 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
@@ -4112,7 +4118,6 @@ 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;
@@ -4132,10 +4137,10 @@ find_idlest_group(struct sched_domain *sd, struct task_struct *p, int this_cpu)
for_each_cpu(i, sched_group_cpus(group)) {
/* Bias balancing toward cpus of our domain */
- if (local_group)
+ if (i == this_cpu)
load = source_load(i);
else
- load = target_load(i);
+ load = target_load(i, sd->imbalance_pct);
avg_load += load;
}
@@ -4151,7 +4156,7 @@ find_idlest_group(struct sched_domain *sd, struct task_struct *p, int this_cpu)
}
} while (group = group->next, group != sd->groups);
- if (!idlest || 100*this_load < imbalance*min_load)
+ if (!idlest || this_load < min_load)
return NULL;
return idlest;
}
@@ -5476,9 +5481,9 @@ static inline void update_sg_lb_stats(struct lb_env *env,
nr_running = rq->nr_running;
- /* Bias balancing toward cpus of our domain */
- if (local_group)
- load = target_load(i);
+ /* Bias balancing toward dst cpu */
+ if (env->dst_cpu == i)
+ load = target_load(i, env->sd->imbalance_pct);
else
load = source_load(i);
@@ -5918,14 +5923,6 @@ static struct sched_group *find_busiest_group(struct lb_env *env)
if ((local->idle_cpus < busiest->idle_cpus) &&
busiest->sum_nr_running <= busiest->group_weight)
goto out_balanced;
- } else {
- /*
- * In the CPU_NEWLY_IDLE, CPU_NOT_IDLE cases, use
- * imbalance_pct to be conservative.
- */
- if (100 * busiest->avg_load <=
- env->sd->imbalance_pct * local->avg_load)
- goto out_balanced;
}
force_balance:
--
1.8.1.2
--
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