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Date: Wed, 4 Dec 2013 17:06:15 +0800
From: Yuanhan Liu <yuanhan.liu@...ux.intel.com>
To: Alex Shi <alex.shi@...aro.org>
Cc: mingo@...hat.com, peterz@...radead.org, morten.rasmussen@....com,
vincent.guittot@...aro.org, daniel.lezcano@...aro.org,
fweisbec@...il.com, linux@....linux.org.uk, tony.luck@...el.com,
fenghua.yu@...el.com, tglx@...utronix.de,
akpm@...ux-foundation.org, arjan@...ux.intel.com, pjt@...gle.com,
fengguang.wu@...el.com, james.hogan@...tec.com, jason.low2@...com,
gregkh@...uxfoundation.org, hanjun.guo@...aro.org,
linux-kernel@...r.kernel.org, Huang Ying <ying.huang@...el.com>
Subject: Re: [PATCH 4/4] sched: bias to target cpu load to reduce task moving
On Tue, Dec 03, 2013 at 05:05:56PM +0800, Alex Shi wrote:
> 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.shi@...aro.org>
Hi Alex,
We obsevered 150% performance gain with vm-scalability/300s-mmap-pread-seq
testcase with this patch applied. Here is a list of changes we got so far:
testbox : brickland
testcase: vm-scalability/300s-mmap-pread-seq
f1b6442c7dd12802e622 d70495ef86f397816d73
(parent commit) (this commit)
------------------------ ------------------------
26393249.80 +150.9% 66223933.60 vm-scalability.throughput
225.12 -49.9% 112.75 time.elapsed_time
36333.40 -90.7% 3392.20 vmstat.system.cs
2.40 +375.0% 11.40 vmstat.cpu.id
3770081.60 -97.7% 87673.40 time.major_page_faults
3975276.20 -97.0% 117409.60 time.voluntary_context_switches
3.05 +301.7% 12.24 iostat.cpu.idle
21118.41 -70.3% 6277.19 time.system_time
18.40 +130.4% 42.40 vmstat.cpu.us
77.00 -41.3% 45.20 vmstat.cpu.sy
47459.60 -31.3% 32592.20 vmstat.system.in
82435.40 -12.1% 72443.60 time.involuntary_context_switches
5128.13 +14.0% 5848.30 time.user_time
11656.20 -7.8% 10745.60 time.percent_of_cpu_this_job_got
1069997484.80 +0.3% 1073679919.00 time.minor_page_faults
--yliu
> ---
> 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
>
> --
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