Return-path: Received: from casper.infradead.org ([85.118.1.10]:44726 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752917AbZJIHKd (ORCPT ); Fri, 9 Oct 2009 03:10:33 -0400 Subject: Re: [.32-rc3] scheduler: iwlagn consistently high in "waiting for CPU" From: Peter Zijlstra To: Mike Galbraith Cc: Frans Pop , Arjan van de Ven , Linux Kernel Mailing List , Ingo Molnar , linux-wireless@vger.kernel.org In-Reply-To: <1255070103.7639.30.camel@marge.simson.net> References: <200910051500.55875.elendil@planet.nl> <200910081655.37485.elendil@planet.nl> <1255026217.6643.12.camel@marge.simson.net> <200910082259.35204.elendil@planet.nl> <1255070103.7639.30.camel@marge.simson.net> Content-Type: text/plain Date: Fri, 09 Oct 2009 09:13:53 +0200 Message-Id: <1255072433.26976.351.camel@twins> Mime-Version: 1.0 Sender: linux-wireless-owner@vger.kernel.org List-ID: On Fri, 2009-10-09 at 08:35 +0200, Mike Galbraith wrote: > > sched: update the clock of runqueue select_task_rq() selected. > > In try_to_wake_up(), we update the runqueue clock, but select_task_rq() > may select a different runqueue than the one we updated, leaving the new > runqueue's clock stale for a bit. > > This patch cures occasional huge latencies reported by latencytop when > coming out of idle on a mostly idle NO_HZ box. > > Signed-off-by: Mike Galbraith > Cc: Ingo Molnar > Cc: Peter Zijlstra Awesome catch Mike, seems I goofed up in my recent ttwu changes. Acked-by: Peter Zijlstra > > --- > kernel/sched.c | 8 ++++++-- > 1 file changed, 6 insertions(+), 2 deletions(-) > > Index: linux-2.6/kernel/sched.c > =================================================================== > --- linux-2.6.orig/kernel/sched.c > +++ linux-2.6/kernel/sched.c > @@ -2311,7 +2311,7 @@ static int try_to_wake_up(struct task_st > { > int cpu, orig_cpu, this_cpu, success = 0; > unsigned long flags; > - struct rq *rq; > + struct rq *rq, *orig_rq; > > if (!sched_feat(SYNC_WAKEUPS)) > wake_flags &= ~WF_SYNC; > @@ -2319,7 +2319,7 @@ static int try_to_wake_up(struct task_st > this_cpu = get_cpu(); > > smp_wmb(); > - rq = task_rq_lock(p, &flags); > + rq = orig_rq = task_rq_lock(p, &flags); > update_rq_clock(rq); > if (!(p->state & state)) > goto out; > @@ -2350,6 +2350,10 @@ static int try_to_wake_up(struct task_st > set_task_cpu(p, cpu); > > rq = task_rq_lock(p, &flags); > + > + if (rq != orig_rq) > + update_rq_clock(rq); > + > WARN_ON(p->state != TASK_WAKING); > cpu = task_cpu(p); > > > >