linux-kernel - Re: [PATCH v3 1/6] measure exec

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Message-ID: <4FC5F727.2040804@parallels.com>
Date:	Wed, 30 May 2012 14:32:07 +0400
From:	Glauber Costa <glommer@...allels.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	<linux-kernel@...r.kernel.org>, <cgroups@...r.kernel.org>,
	<devel@...nvz.org>, Paul Turner <pjt@...gle.com>,
	Tejun Heo <tj@...nel.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	<handai.szj@...il.com>, <Andrew.Phillips@...x.com>,
	Serge Hallyn <serge.hallyn@...onical.com>
Subject: Re: [PATCH v3 1/6] measure exec_clock for rt sched entities

On 05/30/2012 02:29 PM, Peter Zijlstra wrote:
> On Wed, 2012-05-30 at 13:48 +0400, Glauber Costa wrote:
>> For simetry with the cfq tasks, measure exec_clock for the rt
>> sched entities (rt_se).
>
> Symmetry methinks..

=p bad me
> anyway, where is the symmetry?, fair.c:update_curr()
> doesn't do the for_each_sched_entity() thing.

It does implicitly, because fair.c:update_curr() is called from
within enqueue_task(), that is called for_each_sched_entity in
enqueue_task_fair().

>
>> This can be used in a number of fashions. For instance, to
>> compute total cpu usage in a cgroup that is generated by
>> rt tasks.
>>
>> Signed-off-by: Glauber Costa<glommer@...allels.com>
>> CC: Peter Zijlstra<a.p.zijlstra@...llo.nl>
>> CC: Paul Turner<pjt@...gle.com>
>> ---
>>   kernel/sched/rt.c    |    5 +++++
>>   kernel/sched/sched.h |    1 +
>>   2 files changed, 6 insertions(+)
>>
>> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
>> index c5565c3..30ee4e2 100644
>> --- a/kernel/sched/rt.c
>> +++ b/kernel/sched/rt.c
>> @@ -919,6 +919,11 @@ static void update_curr_rt(struct rq *rq)
>>
>>   	sched_rt_avg_update(rq, delta_exec);
>>
>> +	for_each_sched_rt_entity(rt_se) {
>> +		rt_rq = rt_rq_of_se(rt_se);
>> +		schedstat_add(rt_rq, exec_clock, delta_exec);
>> +	}
>> +
>>   	if (!rt_bandwidth_enabled())
>>   		return;
>
> See, this just makes me sad.. you now have a double
> for_each_sched_rt_entity() loop.

The way I read the rt.c code, it it is called from enqueue_task_rt only 
once.
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