Messages in this thread | | | Date | Thu, 12 Mar 2009 14:29:41 -0700 | From | Darren Hart <> | Subject | Re: [tip:core/futexes] futex: use current->time_slack_ns for rt tasks too |
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Peter Zijlstra wrote: > On Thu, 2009-03-12 at 06:53 -0700, Arjan van de Ven wrote: >> Darren Hart wrote: >>> Commit-ID: 16f4993f4e9860715918efd4eeac928f8de1218b >>> Gitweb: http://git.kernel.org/tip/16f4993f4e9860715918efd4eeac928f8de1218b >>> Author: "Darren Hart" <dvhltc@us.ibm.com> >>> AuthorDate: Thu, 12 Mar 2009 00:55:59 -0700 >>> Commit: Ingo Molnar <mingo@elte.hu> >>> CommitDate: Thu, 12 Mar 2009 11:20:57 +0100 >>> >>> futex: use current->time_slack_ns for rt tasks too >>> >>> RT tasks should set their timer slack to 0 on their own. This >>> patch removes the 'if (rt_task()) slack = 0;' block in >>> futex_wait. >> Hi, >> >> can you explain the rationale for this reasoning? > > Yeah, I found it iffy as well, I think we want something like the below > instead though.. > > --- > > 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.
Fork takes care of this by setting the child's default_timer_slack_ns to current->timer_slack_ns. This change takes care of tasks that are converted to rt by the user.
What about tasks that are demoted from RT to SCHED_NORMAL? I'm not sure setting it to the default_timer_slack_ns is the right thing since that could have been the timer_slack_ns of the rt process it forked from. Perhaps heach scheduler class needs to have a default_timer_slack_ns set in the class?
> > 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; > } >
-- Darren Hart IBM Linux Technology Center Real-Time Linux Team
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