linux-kernel - Re: [PATCH] Fix delay accounting regression

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Date:	Fri, 02 Nov 2007 22:05:29 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Fix delay accounting regression

Ingo Molnar wrote:
> * Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:
> 
>> Fix the delay accounting regression introduced by commit 
>> 75d4ef16a6aa84f708188bada182315f80aab6fa. rq no longer has sched_info 
>> data associated with it. task_struct sched_info structure is used by 
>> delay accounting to provide back statistics to user space.
> 
> no, this really is broken code. sched_clock() is not a generally 
> reliable time source so at a minimum the rq->clock fix i mentioned is 
> needed. What user-space tools are utilizing delay-accounting by the way? 

Applications I can think of are

1. iotop
2. Some typical applications are mentioned in
   https://ols2006.108.redhat.com/2007/Reprints/nagar-Reprint.pdf

> We have most of this data available under SCHEDSTATS - how about 
> consolidating CONFIG_TASK_DELAY_ACCT into CONFIG_SCHEDSTATS?
> 
> 	Ingo


Yes, we do use schedstats - except for two cases that I know of?

1. To accumulate information in taskstats to share with user space
   (we copy the data from schedstats into taskstats)
2. We accumulate the data for dead threads in a thread group

-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL
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