Re: Memory mapped IO vs Port IO

[Matthew Wilcox]

On Thu, Sep 11, 2003 at 06:17:02PM +0200, Andi Kleen wrote:
> The overhead of checking for PIO vs mmio at runtime in the drivers
> should be completely in the noise on any non ancient CPU (both MMIO
> and PIO typically take hundreds or thousands of CPU cycles for the bus
> access, having an dynamic function call or an if before that is makes
> no difference at all)

That's not true for MMIO writes which are posted.  They should take
no longer than a memory write.  For MMIO reads and PIO reads & writes,
you are, of course, correct.

-- 
"It's not Hollywood.  War is real, war is primarily not about defeat or
victory, it is about death.  I've seen thousands and thousands of dead bodies.
Do you think I want to have an academic debate on this subject?" -- Robert Fisk
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/