Re: [PATCH] per-interrupt stacks - try 2

[Ingo Molnar <mingo@redhat.com>]

On Thu, 12 Sep 2002, David Howells wrote:

> > per-CPU per-IRQ i mean, of course. It's a basic performance issue, on
> > SMP we do not want dirty IRQ stacks to bounce between CPUs ...
> 
> Do you have benchmarks or something to show that is this actually a
> _significant_ problem?

you need benchmarks to tell that pure per-IRQ stacks are bad for SMP
performance?

per-IRQ+per-CPU and pure per-CPU IRQ stacks should perform rougly equally
well on SMP - with per-CPU IRQ stacks having lower runtime setup cost.

> After all, unless you bind the interrupts to particular IRQs, loads of
> data - including the irq_desc[] table - are going to be bouncing too.

there's a difference between bouncing 1-2 cachelines and bouncing a *full,
dirtied stack*. The irq_desc[] bouncing is pretty much unavoidable (IRQs
do need some global state) - the stack bouncing is just plain stupid and
perfectly avoidable.

	Ingo