linux-kernel - Re: [PATCH] fix granularity of task

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Date:	Thu, 12 Nov 2009 16:00:38 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Stanislaw Gruszka <sgruszka@...hat.com>
Cc:	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>,
	Américo Wang <xiyou.wangcong@...il.com>,
	Spencer Candland <spencer@...ehost.com>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH] fix granularity of task_u/stime(), v2

On Thu, 2009-11-12 at 15:49 +0100, Stanislaw Gruszka wrote:
>  I can not reproduce
> the bug with below patch:
> 
> diff --git a/kernel/exit.c b/kernel/exit.c
> index f7864ac..b85e384 100644
> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -110,8 +110,8 @@ static void __exit_signal(struct task_struct *tsk)
>  		 * We won't ever get here for the group leader, since it
>  		 * will have been the last reference on the signal_struct.
>  		 */
> -		sig->utime = cputime_add(sig->utime, task_utime(tsk));
> -		sig->stime = cputime_add(sig->stime, task_stime(tsk));
> +		sig->utime = cputime_add(sig->utime, tsk->utime); //task_utime(tsk));
> +		sig->stime = cputime_add(sig->stime, tsk->stime); //task_stime(tsk));
>  		sig->gtime = cputime_add(sig->gtime, task_gtime(tsk));
>  		sig->min_flt += tsk->min_flt;
>  		sig->maj_flt += tsk->maj_flt;

Yes, this is the thing I suggested and makes sense.

> diff --git a/kernel/sys.c b/kernel/sys.c
> index ce17760..8be5b75 100644
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -914,8 +914,8 @@ void do_sys_times(struct tms *tms)
>  	struct task_cputime cputime;
>  	cputime_t cutime, cstime;
>  
> -	thread_group_cputime(current, &cputime);
>  	spin_lock_irq(&current->sighand->siglock);
> +	thread_group_cputime(current, &cputime);
>  	cutime = current->signal->cutime;
>  	cstime = current->signal->cstime;
>  	spin_unlock_irq(&current->sighand->siglock);
> 
> Perhaps we can remove task_{u,s}time() in some places or maybe at whole ?

I think task_[us]time() still has value for getrusage() since it avoids
the task hiding from top by never running during the tick crap.

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