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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>
This commit is contained in:
Christoph Lameter 2010-12-14 10:28:45 -06:00 committed by Tejun Heo
parent 05c2d088d0
commit 20b876918c
1 changed files with 9 additions and 9 deletions
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18
kernel/irq_work.c
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@ -77,21 +77,21 @@ void __weak arch_irq_work_raise(void)
*/
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 @@ EXPORT_SYMBOL_GPL(irq_work_queue);
*/
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;