UML - An idle system should have zero load average

The ever-vigilant users of linode.com noticed that an idle 2.6 UML has a persistent load average of ~.4.

It turns out that because the UML timer handler processed softirqs before actually delivering the tick, the tick was counted in the context of the idle thread about half the time.

--

 arch/um/kernel/time.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Index: linux-2.6.21-mm/arch/um/kernel/time.c
===================================================================
@@ -177,6 +177,8 @@ int do_settimeofday(struct timespec *tv)
 
 void timer_handler(int sig, union uml_pt_regs *regs)
 {
+	if(current_thread->cpu == 0)
+		timer_irq(regs);
 	local_irq_disable();
 	irq_enter();
 	update_process_times(CHOOSE_MODE(

@@ -184,6 +186,4 @@ void timer_handler(int sig, union uml_pt
 			     (regs)->skas.is_user));
 	irq_exit();
 	local_irq_enable();
-	if(current_thread->cpu == 0)
-		timer_irq(regs);
 }

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