Messages in this thread | | | Subject | Re: [PATCH] sched: Initialize rq->age_stamp on processor start | From | Mike Galbraith <> | Date | Tue, 18 Mar 2014 05:06:26 +0100 |
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CC maintainer improves patch aerodynamics.
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(); > } > > #ifdef CONFIG_DEBUG_ATOMIC_SLEEP
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