Messages in this thread | | | Date | Tue, 10 Sep 2013 15:02:58 -0700 | Subject | Re: [PATCH 0/7] preempt_count rework -v2 | From | Linus Torvalds <> |
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On Tue, Sep 10, 2013 at 2:51 PM, H. Peter Anvin <hpa@zytor.com> wrote: > On 09/10/2013 02:43 PM, Linus Torvalds wrote: > > Actually, the right thing here really is "er" (which I think you meant, > but just to make it clear.)
Yes, I was just answering the i-vs-e confusion.
> "e" doesn't work on versions of gcc older than the first x86-64 release, > but we don't care about that anymore.
Indeed.
> A final good question is if we should encapsulate the add/inc and > sub/dec into a single function; one could easily do somethin glike:
Yes. However, I would do that at a higher level than the one that builds the actual functions.
That said, there's a few cases where you might want to specify add-vs-sub explicitly, but they are rather odd, namely the fact that "-128" fits in a byte, but "128" does not.
So it can be better to add 128 by doing a "subl $-128" than by doing an "add $128".
But we probably don't have any situation where we care about that special value of "128". I've seen the trick, though.
Linus
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