Re: Add prefetch switch stack hook in scheduler function

From: Ingo Molnar
Date: Thu Jul 28 2005 - 04:18:15 EST

* Nick Piggin <nickpiggin@xxxxxxxxxxxx> wrote:

> >>Just a minor point, I agree with David: I'd like it to be called
> >>prefetch_task(), because some architecture may want to prefetch other
> >>memory.
> >
> >such as?
> Not sure. thread_info? Maybe next->timestamp or some other fields in
> next, something in next->mm?

next->thread_info we could and should prefetch - but from the generic
scheduler code (see the patch i just sent).

i'm not sure what you mean by prefetching next->timestamp, it's an
inline field to 'next', in the first cacheline of it, which we've
already used so it's present. (If you mean the value of next->timestamp,
that has no address meaning at all so would lead to unpredictable
results on some arches.)

next->mm we might want to prefetch, but it's probably not worth it
because we are referencing it too soon, in context_switch(). (while the
kernel stack itself wont be referenced until the full context-switch is
done) But might be worth trying - but even then, it should be done from
the generic code, like the thread_info and kernel-stack prefetching.

> I didn't really have a concrete example, but in the interests of being
> future proof...

i'd like to keep generic bits in generic code, and only move things to
per-arch include files if absolutely necessary. next->mm is generic.

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