linux-kernel - Re: [RFC,PATCH 1/2] cputimers/proc: do_task_stat()->task

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Message-ID: <20100326073723.GA2596@dhcp-lab-161.englab.brq.redhat.com>
Date:	Fri, 26 Mar 2010 08:37:24 +0100
From:	Stanislaw Gruszka <sgruszka@...hat.com>
To:	Balbir Singh <balbir@...ux.vnet.ibm.com>
Cc:	Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Americo Wang <xiyou.wangcong@...il.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Roland McGrath <roland@...hat.com>,
	Spencer Candland <spencer@...ehost.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC,PATCH 1/2] cputimers/proc: do_task_stat()->task_times()
	can race with getrusage()

On Fri, Mar 26, 2010 at 09:23:44AM +0530, Balbir Singh wrote:
> * Oleg Nesterov <oleg@...hat.com> [2010-03-24 21:45:50]:
> 
> > do_task_stat()->task_times() can race with getrusage(), they both can
> > try to update task->prev_Xtime at the same time.
> > 
> > Remove this bit of d180c5bc "sched: Introduce task_times() to replace
> > task_{u,s}time()".
> 
> One of the reasons for adding this accuracy was to avoid sampling
> based noise and errors that occur with utime and stime.
> 
> As long as there is no preemption during the assignment, I think we
> should be OK. 
> 
> I see two options
> 
> 1. Disable preemption around assignment
That one sounds very good.

> 2. Remove task_times() from getrusage()
We want more accurate and what more important monotonic values
in getrusage.

Stanislaw
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