Currently we don't support migration of currently running timers. Current code
flow in __mod_timer() is:
- Find a cpu where we should migrate the timer
- Check if timer is currently running
- If yes, don't migrate.
In this process, the first step is a unnecessary activiy, if the timer is
currently running. This patch tries to avoid it in such cases.
Signed-off-by: Viresh Kumar <viresh.ku...@linaro.org>
---
kernel/timer.c | 26 +++++++++++++-------------
1 file changed, 13 insertions(+), 13 deletions(-)
diff --git a/kernel/timer.c b/kernel/timer.c
index 8c5e7b9..6e5bf98 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -755,23 +755,23 @@ __mod_timer(struct timer_list *timer, unsigned long
expires,
debug_activate(timer, expires);
- cpu = smp_processor_id();
+ /*
+ * Should we try to migrate timer?
+ * However we can't change timer's base while it is running, otherwise
+ * del_timer_sync() can't detect that the timer's handler yet has not
+ * finished. This also guarantees that the timer is serialized wrt
+ * itself.
+ */
+ if (likely(base->running_timer != timer)) {
+ cpu = smp_processor_id();
#if defined(CONFIG_NO_HZ) && defined(CONFIG_SMP)
- if (!pinned && get_sysctl_timer_migration() && idle_cpu(cpu))
- cpu = get_nohz_timer_target();
+ if (!pinned && get_sysctl_timer_migration() && idle_cpu(cpu))
+ cpu = get_nohz_timer_target();
#endif
- new_base = per_cpu(tvec_bases, cpu);
+ new_base = per_cpu(tvec_bases, cpu);
- if (base != new_base) {
- /*
- * We are trying to schedule the timer on the local CPU.
- * However we can't change timer's base while it is running,
- * otherwise del_timer_sync() can't detect that the timer's
- * handler yet has not finished. This also guarantees that
- * the timer is serialized wrt itself.
- */
- if (likely(base->running_timer != timer)) {
+ if (base != new_base) {
/* See the comment in lock_timer_base() */
timer_set_base(timer, NULL);
spin_unlock(&base->lock);
--
1.7.12.rc2.18.g61b472e
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