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Subject: Re: [RFC PATCH] tg: count the sum wait time of an task group
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Ingo Molnar <mingo@redhat.com>, linux-kernel@vger.kernel.org
References: <5c4c978d-e8fb-4bcb-b942-3c6d3dcfc13e@linux.alibaba.com>
 <20180702120356.GJ2494@hirez.programming.kicks-ass.net>
From:   =?UTF-8?B?546L6LSH?= <yun.wang@linux.alibaba.com>
Message-ID: <21628e16-5d34-d7f6-8c10-ff354b4e7b35@linux.alibaba.com>
Date:   Tue, 3 Jul 2018 10:10:05 +0800
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Hi, Peter

On 2018/7/2 下午8:03, Peter Zijlstra wrote:
> On Mon, Jul 02, 2018 at 03:29:39PM +0800, 王贇 wrote:
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index 1866e64..ef82ceb 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -862,6 +862,7 @@ static void update_curr_fair(struct rq *rq)
>>   static inline void
>>   update_stats_wait_end(struct cfs_rq *cfs_rq, struct sched_entity *se)
>>   {
>> +	struct task_group *tg;
>>   	struct task_struct *p;
>>   	u64 delta;
>>
>> @@ -882,6 +883,9 @@ static void update_curr_fair(struct rq *rq)
>>   			return;
>>   		}
>>   		trace_sched_stat_wait(p, delta);
>> +	} else {
>> +		tg = group_cfs_rq(se)->tg;
>> +		__schedstat_add(tg->wait_sum, delta);
>>   	}
> 
> You're joking right? This patch is both broken and utterly insane.
> 
> You're wanting to update an effectively global variable for every
> schedule action (and its broken because it is without any serialization
> or atomics).

Thanks for the reply and sorry for the thoughtless, I'll rewrite
the code to make it per-cpu variable, then assemble the results
on show.

Regards,
Michael Wang


> 
> NAK
>