Re: Memory mapped IO vs Port IO

Jamie Lokier
2003-09-11T17:13:28Z

Andi Kleen wrote:
> My gut feeling is to just fix the drivers to make this runtime switchable
> and get rid of the compile time options.
>
> This would help distributions (who normally want to build conservative
> by default, but still allow the users easy tuning without recompilation)
> For that it would be nice if a standard module parameter or maybe
> sysfs option existed.

Another way to help distributions is to compile those drivers twice,
once for each access type. There aren't all that many drivers that
need it.

> 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)

Ah, but what about the ancient CPUs?

-- Jamie