linux-kernel - Re: [PATCH/RFC] do not count frozen tasks toward load

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Message-Id: <20090408175702.8a99c803.akpm@linux-foundation.org>
Date:	Wed, 8 Apr 2009 17:57:02 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Nathan Lynch <ntl@...ox.com>
Cc:	linux-kernel@...r.kernel.org,
	containers@...ts.linux-foundation.org,
	linux-pm@...ts.linux-foundation.org, Ingo Molnar <mingo@...e.hu>,
	Matt Helsley <matthltc@...ibm.com>
Subject: Re: [PATCH/RFC] do not count frozen tasks toward load

On Wed, 8 Apr 2009 19:45:12 -0500 Nathan Lynch <ntl@...ox.com> wrote:

> Freezing tasks via the cgroup freezer causes the load average to climb
> because the freezer's current implementation puts frozen tasks in
> uninterruptible sleep (D state).
> 
> Some applications which perform job-scheduling functions consult the
> load average when making decisions.  If a cgroup is frozen, the load
> average does not provide a useful measure of the system's utilization
> to such applications.  This is especially inconvenient if the job
> scheduler employs the cgroup freezer as a mechanism for preempting low
> priority jobs.  Contrast this with using SIGSTOP for the same purpose:
> the stopped tasks do not count toward system load.
> 
> Change task_contributes_to_load() to return false if the task is
> frozen.  This results in /proc/loadavg behavior that better meets
> users' expectations.
> 
> Signed-off-by: Nathan Lynch <ntl@...ox.com>
> ---
>  include/linux/sched.h |    3 ++-
>  1 files changed, 2 insertions(+), 1 deletions(-)
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 011db2f..f8af167 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -202,7 +202,8 @@ extern unsigned long long time_sync_thresh;
>  #define task_is_stopped_or_traced(task)	\
>  			((task->state & (__TASK_STOPPED | __TASK_TRACED)) != 0)
>  #define task_contributes_to_load(task)	\
> -				((task->state & TASK_UNINTERRUPTIBLE) != 0)
> +				((task->state & TASK_UNINTERRUPTIBLE) != 0 && \
> +				 (task->flags & PF_FROZEN) == 0)
>  
>  #define __set_task_state(tsk, state_value)		\
>  	do { (tsk)->state = (state_value); } while (0)

Looks OK to me.  It should perhaps use !frozen(task), but the includes
are mucked up.

I suppose we should fix this in -stable too.
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