Re: [PATCH] local_irq_disable removal

Ingo Molnar
2005-06-12T06:58:16Z

* Thomas Gleixner <tglx@linutronix.de> wrote:

> On Sat, 2005-06-11 at 13:51 -0700, Daniel Walker wrote:
> > On Sat, 11 Jun 2005, Ingo Molnar wrote:
>
> > Interesting .. So "cli" takes 7 cycles , "sti" takes 7 cycles. The current
> > method does "lea" which takes 1 cycle, and "or" which takes 1 cycle. I'm
> > not sure if there is any function call overhead .. So the soft replacment
> > of cli/sti is 70% faster on a per instruction level .. So it's at least
> > not any slower .. Does everyone agree on that?
>
> No, because x86 is not the whole universe

x86 is actually a 'worst-case', because it has one of the cheapest CPU
level cli/sti implementations. Usually it's the hard-local_irq_disable()
overhead on non-x86 platforms that is a problem. (ARM iirc) So in this
sense the soft-flag should be a win on most sane architectures.

Ingo