On Wed, 21 Aug 2013 10:08:30 +0200
Jan Kara <j...@suse.cz> wrote:
> struct irq_work {
> unsigned long flags;
> diff --git a/kernel/irq_work.c b/kernel/irq_work.c
> index 55fcce6..446cd81 100644
> --- a/kernel/irq_work.c
> +++ b/kernel/irq_work.c
> @@ -22,6 +22,9 @@
> static DEFINE_PER_CPU(struct llist_head, irq_work_list);
> static DEFINE_PER_CPU(int, irq_work_raised);
>
> +/* List of irq-work any CPU can pick up */
> +static LLIST_HEAD(unbound_irq_work_list);
> +
> /*
> * Claim the entry so that no one else will poke at it.
> */
> @@ -70,12 +73,16 @@ void irq_work_queue(struct irq_work *work)
> /* Queue the entry and raise the IPI if needed. */
> preempt_disable();
>
> - llist_add(&work->llnode, &__get_cpu_var(irq_work_list));
> + if (!(work->flags & __IRQ_WORK_UNBOUND))
> + llist_add(&work->llnode, &__get_cpu_var(irq_work_list));
> + else
> + llist_add(&work->llnode, &unbound_irq_work_list);
Just for better readability I would have:
if (work->flags & __IRQ_WORK_UNBOUND)
llist_add(&work->llnode, &unbound_irq_work_list);
else
llist_add(&work->llnode, &__get_cpu_var(irq_work_list));
>
> /*
> * If the work is not "lazy" or the tick is stopped, raise the irq
> * work interrupt (if supported by the arch), otherwise, just wait
> - * for the next tick.
> + * for the next tick. We do this even for unbound work to make sure
> + * *some* CPU will be doing the work.
> */
> if (!(work->flags & IRQ_WORK_LAZY) || tick_nohz_tick_stopped()) {
> if (!this_cpu_cmpxchg(irq_work_raised, 0, 1))
> @@ -100,28 +107,11 @@ bool irq_work_needs_cpu(void)
> return true;
> }
>
> -static void __irq_work_run(void)
> +static void process_irq_work_list(struct llist_node *llnode)
> {
> unsigned long flags;
> struct irq_work *work;
> - struct llist_head *this_list;
> - struct llist_node *llnode;
> -
> -
> - /*
> - * Reset the "raised" state right before we check the list because
> - * an NMI may enqueue after we find the list empty from the runner.
> - */
> - __this_cpu_write(irq_work_raised, 0);
> - barrier();
>
> - this_list = &__get_cpu_var(irq_work_list);
> - if (llist_empty(this_list))
> - return;
> -
> - BUG_ON(!irqs_disabled());
> -
> - llnode = llist_del_all(this_list);
> while (llnode != NULL) {
> work = llist_entry(llnode, struct irq_work, llnode);
>
> @@ -146,6 +136,27 @@ static void __irq_work_run(void)
> }
> }
>
> +static void __irq_work_run(void)
> +{
> + struct llist_head *this_list;
> +
> + /*
> + * Reset the "raised" state right before we check the list because
> + * an NMI may enqueue after we find the list empty from the runner.
> + */
> + __this_cpu_write(irq_work_raised, 0);
> + barrier();
> +
> + this_list = &__get_cpu_var(irq_work_list);
> + if (llist_empty(this_list) && llist_empty(&unbound_irq_work_list))
> + return;
> +
> + BUG_ON(!irqs_disabled());
> +
> + process_irq_work_list(llist_del_all(this_list));
> + process_irq_work_list(llist_del_all(&unbound_irq_work_list));
OK, I'm being a bit of an micro optimization freak here, but...
How about moving the list_empty() and BUG_ON into the
process_irq_work_list() call.
That is,
if (list_empty(llnode))
return;
BUG_ON(!irqs_disabled());
That way we avoid the double xchg() that is done with the two calls to
llist_del_all().
-- Steve
> +}
> +
> /*
> * Run the irq_work entries on this cpu. Requires to be ran from hardirq
> * context with local IRQs disabled.
--
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