Messages in this thread | | | Date | Tue, 18 Mar 2014 09:56:12 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH] sched: Initialize rq->age_stamp on processor start |
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On Tue, Mar 18, 2014 at 05:06:26AM +0100, Mike Galbraith wrote: > CC maintainer improves patch aerodynamics.
hehe, for sure. I have very little time to look at lkml these days and there's a near 100% chance I'll miss anything that doesn't hit the inbox.
> On Mon, 2014-03-17 at 19:05 -0500, minyard@acm.org wrote: > > From: Corey Minyard <cminyard@mvista.com> > > > > 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 <cminyard@mvista.com> > > --- > > 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();
I would put it one line up; that scheduler_running=1 is the last thing we should do.
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