Re: [RFC] per-cpu preempt_count

[Linus Torvalds]

On Tue, Aug 13, 2013 at 5:26 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>
> So we're now down to something like:
>
>   decl fs:preempt_count
>   cmpl PREEMPT_NEED_RESCHED,fs:preempt_count
>   jnz 1f

Well, this isn't worth doing unless you can make PREEMPT_NEED_RESCHED
be the high bit, and we can combine it into just "decl+jns". Otherwise
we'd be better off with the simpler two separate adjacent variables.

Also, I think your patch is too big, and you should have aim to just
made the "preempt_count()" helper function mask off PREEMPT_MASK, so
that you don't change the semantics of that. I realize that there are
a couple of users that do things like "preempt_count() += x", and you
probably wanted to keep those working, but I think it is easier (and
cleaner) to fix those to "preempt_count_update(x)" instead of adding
all those explicitly PREEMPT_MASK masks.

Hmm?

             Linus
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