irq_work: Use per cpu atomics instead of regular atomics
The irq work queue is a per cpu object and it is sufficient for
synchronization if per cpu atomics are used. Doing so simplifies
the code and reduces the overhead of the code.
Before:
christoph@linux-2.6$ size kernel/irq_work.o
text data bss dec hex filename
451 8 1 460 1cc kernel/irq_work.o
After:
christoph@linux-2.6$ size kernel/irq_work.o
text data bss dec hex filename
438 8 1 447 1bf kernel/irq_work.o
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Christoph Lameter <cl@linux.com>
diff --git a/kernel/irq_work.c b/kernel/irq_work.c
index 90f8819..c58fa7d 100644
--- a/kernel/irq_work.c
+++ b/kernel/irq_work.c
@@ -77,21 +77,21 @@
*/
static void __irq_work_queue(struct irq_work *entry)
{
- struct irq_work **head, *next;
+ struct irq_work *next;
- head = &get_cpu_var(irq_work_list);
+ preempt_disable();
do {
- next = *head;
+ next = __this_cpu_read(irq_work_list);
/* Can assign non-atomic because we keep the flags set. */
entry->next = next_flags(next, IRQ_WORK_FLAGS);
- } while (cmpxchg(head, next, entry) != next);
+ } while (this_cpu_cmpxchg(irq_work_list, next, entry) != next);
/* The list was empty, raise self-interrupt to start processing. */
if (!irq_work_next(entry))
arch_irq_work_raise();
- put_cpu_var(irq_work_list);
+ preempt_enable();
}
/*
@@ -120,16 +120,16 @@
*/
void irq_work_run(void)
{
- struct irq_work *list, **head;
+ struct irq_work *list;
- head = &__get_cpu_var(irq_work_list);
- if (*head == NULL)
+ if (this_cpu_read(irq_work_list) == NULL)
return;
BUG_ON(!in_irq());
BUG_ON(!irqs_disabled());
- list = xchg(head, NULL);
+ list = this_cpu_xchg(irq_work_list, NULL);
+
while (list != NULL) {
struct irq_work *entry = list;
