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

[Darren Hart]

Arjan van de Ven wrote:
> Peter Zijlstra wrote:
> > > > ---
> > > >
> > > > Subject: sched: adjust timer_slack_ns on scheduler policy change
> > > > From: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
> > > > Date: Thu Mar 12 15:01:02 CET 2009
> > > >
> > > > Ensure RT tasks have 0 timer slack.
> > > >
> > > > Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
> > > > ---
> > > >  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.

It seems to me that changing your scheduling class from userspace would 
be reasonable justification to change the timer slack to a default value 
for that class.  Thoughts?

--
Darren Hart
IBM Linux Technology Center
Real-Time Linux Team
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