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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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