Re: [RFC][PATCH] irq_work -v2

[huang ying <huang.ying.caritas@gmail.com>]

On Sat, Jun 26, 2010 at 2:30 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> +
> +static DEFINE_PER_CPU(struct irq_work *, irq_work_list);
> +
> +/*
> + * Claim the entry so that no one else will poke at it.
> + */
> +static bool irq_work_claim(struct irq_work *entry)
> +{
> +       unsigned long flags;
> +
> +       do {
> +               flags = (unsigned long)entry->next;
> +               if (flags & IRQ_WORK_PENDING)
> +                       return false;
> +       } while (cmpxchg(&entry->next, flags, flags | IRQ_WORK_FLAGS) != flags);
> +
> +       return true;
> +}
> +
> +
> +void __weak arch_irq_work_raise(void)
> +{
> +       /*
> +        * Lame architectures will get the timer tick callback
> +        */
> +}
> +
> +/*
> + * Queue the entry and raise the IPI if needed.
> + */
> +static void __irq_work_queue(struct irq_work *entry)
> +{
> +       struct irq_work **head;
> +
> +       head = &get_cpu_var(irq_work_list);
> +
> +       do {
> +               /*
> +                * Can assign non-atomic because we keep the flags set.
> +                */
> +               entry->next = next_flags(*head, IRQ_WORK_FLAGS);
> +       } while (cmpxchg(head, entry->next, entry) != entry->next);

*head & IRQ_WORK_FLAGS == 0, but entry->next & IRQ_WORK_FLAGS ==
IRQ_WORK_FLAGS. So the cmpxchg will never succeed.

> +
> +       /*
> +        * 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);
> +}

Best Regards,
Huang Ying