[PATCH 3/5] hrtimer: simplify hotplug migration

[Peter Zijlstra]

From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>

No need for a smp function call, which is likely to run on the same
CPU anyway. We can just call hrtimers_peek_ahead() in the interrupts
disabled section of migrate_hrtimers().

Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Acked-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
---
 kernel/hrtimer.c |   25 ++++++++++---------------
 1 file changed, 10 insertions(+), 15 deletions(-)

Index: linux-2.6-tip/kernel/hrtimer.c
===================================================================
--- linux-2.6-tip.orig/kernel/hrtimer.c
+++ linux-2.6-tip/kernel/hrtimer.c
@@ -1505,11 +1505,6 @@ static void __cpuinit init_hrtimers_cpu(
 
 #ifdef CONFIG_HOTPLUG_CPU
 
-static void tickle_timers(void *arg)
-{
-	hrtimer_peek_ahead_timers();
-}
-
 static void migrate_hrtimer_list(struct hrtimer_clock_base *old_base,
 				struct hrtimer_clock_base *new_base)
 {
@@ -1548,20 +1543,19 @@ static void migrate_hrtimer_list(struct 
 static void migrate_hrtimers(int scpu)
 {
 	struct hrtimer_cpu_base *old_base, *new_base;
-	int dcpu, i;
+	int i;
 
 	BUG_ON(cpu_online(scpu));
-	old_base = &per_cpu(hrtimer_bases, scpu);
-	new_base = &get_cpu_var(hrtimer_bases);
-
-	dcpu = smp_processor_id();
-
 	tick_cancel_sched_timer(scpu);
+
+	local_irq_disable();
+	old_base = &per_cpu(hrtimer_bases, scpu);
+	new_base = &__get_cpu_var(hrtimer_bases);
 	/*
 	 * The caller is globally serialized and nobody else
 	 * takes two locks at once, deadlock is not possible.
 	 */
-	spin_lock_irq(&new_base->lock);
+	spin_lock(&new_base->lock);
 	spin_lock_nested(&old_base->lock, SINGLE_DEPTH_NESTING);
 
 	for (i = 0; i < HRTIMER_MAX_CLOCK_BASES; i++) {
@@ -1570,10 +1564,11 @@ static void migrate_hrtimers(int scpu)
 	}
 
 	spin_unlock(&old_base->lock);
-	spin_unlock_irq(&new_base->lock);
-	put_cpu_var(hrtimer_bases);
+	spin_unlock(&new_base->lock);
 
-	smp_call_function_single(dcpu, tickle_timers, NULL, 0);
+	/* Check, if we got expired work to do */
+	__hrtimer_peek_ahead_timers();
+	local_irq_enable();
 }
 
 #endif /* CONFIG_HOTPLUG_CPU */

-- 

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