Re: [RFC PATCH 0/4] sched: remove cpu_load decay.
From: Daniel Lezcano
Date: Tue Nov 26 2013 - 07:36:00 EST
On 11/24/2013 06:29 AM, Alex Shi wrote:
On 11/22/2013 08:13 PM, Daniel Lezcano wrote:
Hi Alex,
I tried on my Xeon server (2 x 4 cores) your patchset and got the
following result:
kernel a5d6e63323fe7799eb0e6 / + patchset
hackbench -T -s 4096 -l 1000 -g 10 -f 40
27.604 38.556
Wondering if the following patch is helpful on your Xeon server?
Btw, you can run vmstat as background tool or use 'perf sched'
to get scheduler statistics change for this patchset.
The following are results of original kernel and all 5 patches
on pandaboard ES.
latest kernel 527d1511310a89 + this patchset
hackbench -T -g 10 -f 40
23.25" 20.79"
23.16" 20.4"
24.24" 20.29"
hackbench -p -g 10 -f 40
26.52" 21.2"
23.89" 24.07"
25.65" 20.30"
hackbench -P -g 10 -f 40
20.14" 19.53"
19.96" 20.37"
21.76" 20.39"
Here the new results with your patchset + patch #5
I have some issues with perf for the moment, so I will fix it up and
send the result after.
527d1511310a / + patchset + #5
hackbench -T -s 4096 -l 1000 -g 10 -f 40
26.677 30.308
27.914 28.497
28.390 30.360
28.048 28.587
26.344 29.513
27.848 28.706
28.315 30.152
28.232 29.721
26.549 28.766
30.340 38.801
hackbench -p -s 4096 -l 1000 -g 10 -f 40
34.522 35.469
34.545 34.966
34.469 35.342
34.115 35.286
34.457 35.592
34.561 35.314
34.459 35.316
34.054 35.629
34.532 35.149
34.459 34.876
hackbench -P -s 4096 -l 1000 -g 10 -f 40
38.938 30.308
39.363 28.497
39.340 30.360
38.909 28.587
39.095 29.513
38.869 28.706
39.041 30.152
38.939 29.721
38.992 28.766
38.947 38.801
------
From 4f5efd6c2b1e7293410ad57c3db24dcf3394c4a3 Mon Sep 17 00:00:00 2001
From: Alex Shi <alex.shi@xxxxxxxxxx>
Date: Sat, 23 Nov 2013 23:18:09 +0800
Subject: [PATCH] sched: aggravate 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 with sd->
imbalance_pct.
Signed-off-by: Alex Shi <alex.shi@xxxxxxxxxx>
---
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);
--
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