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SubjectRe: [PATCH v5 3/7] sched: set initial value of runnable avg for new forked task
On 05/08/2013 07:34 PM, Peter Zijlstra wrote:
>> > If we wanted to be more exacting about it we could just give them a
>> > sched_slice() worth; this would have a few obvious "nice" properties
>> > (pun intended).
> Oh I see I misunderstood again :/ Its not about the effective load but weight
> of the initial effective load wrt adjustment.
>
> Previous schedulers didn't have this aspect at all, so no experience from me
> here. Paul would be the one, since he's ran longest with this stuff.
>
> That said, I would tend to keep it shorter rather than longer so that it would
> adjust quicker to whatever it really wanted to be.
>
> Morten says the load is unstable specifically on loaded systems. I would think
> this is because we'd experience scheduling latency, we're runnable more pushing
> things up. But if we're really an idle task at heart we'd not run again for a
> long while, pushing things down again.
>
> So on that point Paul's suggestion of maybe starting with __sched_slice() might
> make sense because it increases the weight of the initial avg with nr_running.
>
> Not sure really, we'll have to play and see what works best for a number of
> workloads.


The patch of using sched_slice for review, I am testing the benchmarks

---
From da40ffa90ec1de520bd7e92f5653734a964e3bb2 Mon Sep 17 00:00:00 2001
From: Alex Shi <alex.shi@intel.com>
Date: Thu, 9 May 2013 15:28:34 +0800
Subject: [PATCH 4/8] sched: set initial runnable avg for new task

---
kernel/sched/core.c | 2 ++
kernel/sched/fair.c | 15 +++++++++++++++
kernel/sched/sched.h | 2 ++
3 files changed, 19 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index ecec7f1..c17925b 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1716,6 +1716,8 @@ void wake_up_new_task(struct task_struct *p)
set_task_cpu(p, select_task_rq(p, SD_BALANCE_FORK, 0));
#endif

+ /* Give new task a start runnable time */
+ set_task_runnable_avg(p);
rq = __task_rq_lock(p);
activate_task(rq, p, 0);
p->on_rq = 1;
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 2881d42..4ec5f29 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -661,6 +661,21 @@ static u64 sched_vslice(struct cfs_rq *cfs_rq, struct sched_entity *se)
return calc_delta_fair(sched_slice(cfs_rq, se), se);
}

+#ifdef CONFIG_SMP
+void set_task_runnable_avg(struct task_struct *p)
+{
+ u64 slice;
+
+ slice = sched_slice(task_cfs_rq(p), &p->se);
+ p->se.avg.runnable_avg_sum = slice;
+ p->se.avg.runnable_avg_period = slice;
+}
+#else
+void set_task_runnable_avg(struct task_struct *p)
+{
+}
+#endif
+
/*
* Update the current task's runtime statistics. Skip current tasks that
* are not in our scheduling class.
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index c6634f1..518f3d8a 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -900,6 +900,8 @@ extern void init_rt_bandwidth(struct rt_bandwidth *rt_b, u64 period, u64 runtime

extern void update_idle_cpu_load(struct rq *this_rq);

+extern void set_task_runnable_avg(struct task_struct *p);
+
#ifdef CONFIG_CGROUP_CPUACCT
#include <linux/cgroup.h>
/* track cpu usage of a group of tasks and its child groups */
--
1.7.12
--
Thanks
Alex


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