From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750746AbaCREGb (ORCPT ); Tue, 18 Mar 2014 00:06:31 -0400 Received: from mail-ee0-f53.google.com ([74.125.83.53]:64211 "EHLO mail-ee0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750719AbaCREGa (ORCPT ); Tue, 18 Mar 2014 00:06:30 -0400 Message-ID: <1395115586.4883.36.camel@marge.simpson.net> Subject: Re: [PATCH] sched: Initialize rq->age_stamp on processor start From: Mike Galbraith To: minyard@acm.org Cc: linux-kernel@vger.kernel.org, Corey Minyard , Peter Zijlstra Date: Tue, 18 Mar 2014 05:06:26 +0100 In-Reply-To: <1395101149-10097-1-git-send-email-minyard@acm.org> References: <1395101149-10097-1-git-send-email-minyard@acm.org> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.3 Content-Transfer-Encoding: 7bit Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org CC maintainer improves patch aerodynamics. On Mon, 2014-03-17 at 19:05 -0500, minyard@acm.org wrote: > From: Corey Minyard > > If the sched_clock time starts at a large value, the kernel will spin > in sched_avg_update for a long time while rq->age_stamp catches up > with rq->clock. > > The comment in kernel/sched/clock.c says that there is no strict promise > that it starts at zero. So initialize rq->age_stamp when a cpu starts up > to avoid this. > > I was seeing long delays on a simulator that didn't start the clock at > zero. This might also be an issue on reboots on processors that don't > re-initialize the timer to zero on reset, and when using kexec. > > Signed-off-by: Corey Minyard > --- > kernel/sched/core.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index b46131e..5be3d4a 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -5037,11 +5037,20 @@ static struct notifier_block migration_notifier = { > .priority = CPU_PRI_MIGRATION, > }; > > +static void __cpuinit set_cpu_rq_start_time(void) > +{ > + int cpu = smp_processor_id(); > + struct rq *rq = cpu_rq(cpu); > + rq->age_stamp = sched_clock_cpu(cpu); > +} rq->age_stamp must lag rq->clock. See scale_rt_power(), and what happens when it munches magic timewarp mushrooms. > + > static int sched_cpu_active(struct notifier_block *nfb, > unsigned long action, void *hcpu) > { > switch (action & ~CPU_TASKS_FROZEN) { > case CPU_STARTING: > + set_cpu_rq_start_time(); > + /* fall through */ > case CPU_DOWN_FAILED: > set_cpu_active((long)hcpu, true); > return NOTIFY_OK; > @@ -6922,6 +6931,7 @@ void __init sched_init(void) > init_sched_fair_class(); > > scheduler_running = 1; > + set_cpu_rq_start_time(); > } > > #ifdef CONFIG_DEBUG_ATOMIC_SLEEP