From a803f0261bb2bb57aab5542af3174db43b2a3887 Mon Sep 17 00:00:00 2001 From: Corey Minyard Date: Thu, 8 May 2014 13:47:39 -0500 Subject: [PATCH] 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 Signed-off-by: Peter Zijlstra Link: http://lkml.kernel.org/r/1399574859-11714-1-git-send-email-minyard@acm.org Signed-off-by: Ingo Molnar --- kernel/sched/core.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index f5605b6deea4..da302ca98f60 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -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(); -- 2.45.2