Commit a803f026 authored May 08, 2014 by Corey Minyard Committed by Ingo Molnar May 22, 2014

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: Corey Minyard <cminyard@mvista.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1399574859-11714-1-git-send-email-minyard@acm.org


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 72465447

kernel/sched/core.c

+11 −0

Original line number	Diff line number	Diff line
		@@ -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) {
		case CPU_STARTING:
		set_cpu_rq_start_time();
		return NOTIFY_OK;
		case CPU_DOWN_FAILED:
		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);
		idle_thread_set_boot_cpu();
		set_cpu_rq_start_time();
		#endif
		init_sched_fair_class();

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