Re: Memory mapped IO vs Port IO

Matthew Wilcox
2003-09-11T16:25:10Z

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.

--
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