Re: [PATCH] 2.6 workaround for Athlon/Opteron prefetch errata

[Bill Davidsen]

On Mon, 15 Sep 2003, Nick Piggin wrote:

> 
> 
> John Bradford wrote:

> I guess more specialised users would be able to edit the cache line
> size themselves. I wouldn't be adverse to a kconfig setting under the
> embedded menu though.

Clearly something which might be useful for some embedded CPUs.

> I can see an argument for cache line size but thats about it. I can't
> think of my optimisations that should be done on one architecture but
> not another.

Well, if you meant "any optimizations" there are lots, and they already
have config entries. Ex: F.P. emulation, RZ1000 fixups, etc.

> No I definitely agree. Except sometimes you'll have to check at runtime:
> a kernel compiled for all cpus for example needs Andi's Athlon prefetch
> scheme. You'd really want some good helpers to either do runtime check
> or always, or never. Something like this optimises down OK if cpu and
> archmask are constant.
> 
> static inline void ifcpu(const int cpumask, void (*func)(void))
> {
>         if ((cpumask&archmask) && ((~cpumask)&archmask)) {
>                 if (cpumask&current_cpu)
>                         func();
>         } else if (cpumask&archmask) {
>                 func();
>         }
> }
>
> ifcpu(K7||K8, &prefetch_workaround);
> 
> You then need to get kconfig to generate cpu and archmask nicely.
> You obviously still need to ifdef your prefetch_workaround to get the
> space saving.

True, there's no way to get a minimal kernel without at least some
ifdef'iness, although if you defined the code as an inline function and
used your code above... a matter of style, a few preprocessor lines in
that much code aren't going to be confusing.

-- 
bill davidsen <davidsen@xxxxxxx>
  CTO, TMR Associates, Inc
Doing interesting things with little computers since 1979.

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