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Date: Fri, 25 May 2012 09:08:42 -0400 From: Steven Rostedt <rostedt@...dmis.org> To: Peter Zijlstra <a.p.zijlstra@...llo.nl> Cc: Hiroshi Shimamoto <h-shimamoto@...jp.nec.com>, Ingo Molnar <mingo@...e.hu>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: Re: [PATCH 3/3] sched/rt: Remove redundant check before push_rt_task() On Fri, 2012-05-25 at 11:39 +0200, Peter Zijlstra wrote: > On Fri, 2012-05-25 at 15:43 +0900, Hiroshi Shimamoto wrote: > > From: Hiroshi Shimamoto <h-shimamoto@...jp.nec.com> > > > > Currently rq->rt.overloaded is checked twice in switched_to_rt(). > > Remove the first one which out of push_rt_task(). > > Steven was this on purpose to avoid the call or can I apply this thing? > Yeah, I think I added that as a way to avoid the call, but I never did any benchmarks to see if it was actually better (extra check to avoid the call, or just do the call and remove the duplicate check). It would be a good idea to see how ofter that check happens in the real world. As two or more RT tasks on the same CPU is only something that happens on a real RT system (as the common case that is). It's a micro optimization, as a double duplicate check should be fast as everything is nicely in the cache line. But an extra call may be expensive. But it's not a big difference to me if you take the patch or not. > > Signed-off-by: Hiroshi Shimamoto <h-shimamoto@...jp.nec.com> > > --- > > kernel/sched/rt.c | 2 +- > > 1 files changed, 1 insertions(+), 1 deletions(-) > > > > diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c > > index c5565c3..a601a70 100644 > > --- a/kernel/sched/rt.c > > +++ b/kernel/sched/rt.c > > @@ -1907,7 +1907,7 @@ static void switched_to_rt(struct rq *rq, struct task_struct *p) > > */ > > if (p->on_rq && rq->curr != p) { > > #ifdef CONFIG_SMP > > - if (rq->rt.overloaded && push_rt_task(rq) && > > + if (push_rt_task(rq) && > > /* Don't resched if we changed runqueues */ > > rq != task_rq(p)) If you decide to take this patch, it may be better to switch it to: /* Don't resched if we changed runqueues */ if (push_rt_task(rq) && rq != task_rq(p)) -- Steve > > check_resched = 0; > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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