Commit-ID: 6cfa0c323ca96b7f619932725bfc0de1e4a484fc
Gitweb: http://git.kernel.org/tip/6cfa0c323ca96b7f619932725bfc0de1e4a484fc
Author: Corey Minyard <cminyard@xxxxxxxxxx>
AuthorDate: Thu, 8 May 2014 13:47:39 -0500
Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Mon, 19 May 2014 22:02:41 +0900
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.
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Corey Minyard <cminyard@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1399574859-11714-1-git-send-email-minyard@xxxxxxx
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
kernel/sched/core.c | 11 +++++++++++
1 file changed, 11 insertions(+)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 10d9b50..c134eb0 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();
--
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