Re: [tip:core/futexes] futex: use current->time_slack_ns for rt tasks too

[Arjan van de Ven <arjan@linux.intel.com>]

Peter Zijlstra wrote:
>>> ---
>>>
>>> Subject: sched: adjust timer_slack_ns on scheduler policy change
>>> From: Peter Zijlstra <a.p.zijlstra@chello.nl>
>>> Date: Thu Mar 12 15:01:02 CET 2009
>>>
>>> Ensure RT tasks have 0 timer slack.
>>>
>>> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
>>> ---
>>>  kernel/sched.c |    2 ++
>>>  1 file changed, 2 insertions(+)
>>>
>>> Index: linux-2.6/kernel/sched.c
>>> ===================================================================
>>> --- linux-2.6.orig/kernel/sched.c
>>> +++ linux-2.6/kernel/sched.c
>>> @@ -5511,10 +5511,12 @@ __setscheduler(struct rq *rq, struct tas
>>>  	case SCHED_NORMAL:
>>>  	case SCHED_BATCH:
>>>  	case SCHED_IDLE:
>>> +		p->timer_slack_ns = p->default_timer_slack_ns;
>>>  		p->sched_class = &fair_sched_class;
>>>  		break;
>>>  	case SCHED_FIFO:
>>>  	case SCHED_RR:
>>> +		p->timer_slack_ns = 0;
>>>  		p->sched_class = &rt_sched_class;
>>>  		break;
>>>  	}
>>>
> 
> Looking at the default_timer_slack_ns stuff, do we want something like
> the below?

the original idea was that you had a default slack that you got from exec time,
and then something you could just tweak around yourself independently....

this would throw that out of the window.