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

[Nigel Cunningham <ncunningham-lkml@crca.org.au>]

Hi again.

On Wed, 2009-04-08 at 19:45 -0500, Nathan Lynch 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@pobox.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)

Tested-by: Nigel Cunningham <nigel@tuxonice.net>

Looks good to me (though I like Andrew's point about using task_frozen).

nigel@nigel-laptop:~$ cat /proc/loadavg 
0.34 0.27 0.12 1/251 9001
nigel@nigel-laptop:~$ sudo hibernate
nigel@nigel-laptop:~$ cat /proc/loadavg 
0.52 0.33 0.14 2/250 9807
nigel@nigel-laptop:~$