Re: [rfc] direct IO submission and completion scalability issues

Andi Kleen
2008-02-04T10:30:23Z

> + q = &__get_cpu_var(call_single_queue);
> + spin_lock_irqsave(&q->lock, flags);
> + list_replace_init(&q->list, &list);
> + spin_unlock_irqrestore(&q->lock, flags);

I think you could do that lockless if you use a similar data structure
as netchannels (essentially a fixed size single buffer queue with atomic
exchange of the first/last pointers) and not using a list. That would avoid
at least one bounce for the lock and likely another one for the list
manipulation.

Also the right way would be to not add a second mechanism for this,
but fix the standard smp_call_function_single() to support it.

-Andi