Commit a803f026 authored by Corey Minyard's avatar Corey Minyard Committed by Ingo Molnar
Browse files

sched: Initialize rq->age_stamp on processor start

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: default avatarCorey Minyard <>
Signed-off-by: default avatarPeter Zijlstra <>

Signed-off-by: default avatarIngo Molnar <>
parent 72465447
......@@ -5089,10 +5089,20 @@ 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);
static int sched_cpu_active(struct notifier_block *nfb,
unsigned long action, void *hcpu)
switch (action & ~CPU_TASKS_FROZEN) {
return NOTIFY_OK;
set_cpu_active((long)hcpu, true);
return NOTIFY_OK;
......@@ -6970,6 +6980,7 @@ void __init sched_init(void)
if (cpu_isolated_map == NULL)
zalloc_cpumask_var(&cpu_isolated_map, GFP_NOWAIT);
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