Re: [RFC][PATCH 3/2] x86/jump labels: Count and display the short jumps used

From: H. Peter Anvin
Date: Wed Aug 07 2013 - 15:28:50 EST

Well we do... both to extract relocations and to sort the exception table. Perhaps we need to merge those kinds of postprocessing tools?

Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>On Wed, Aug 7, 2013 at 10:54 AM, Steven Rostedt <rostedt@xxxxxxxxxxx>
>> On another box, using a distro config, I had even better results:
>> [ 2.352448] short jumps: 193
>> [ 2.355407] long jumps: 219
>.. well, another way of looking at this is to say that all of this
>effort saves just 579 bytes.
>Yes, maybe some of those bytes are in really hot paths, but the other
>side of *that* coin is that the 2-vs-5 byte jump doesn't much matter
>if it's already cached.
>So I'd vote for not doing this. If we had some simple way to do the
>short jumps, I think it would be lovely. Or if we had to parse the ELF
>files and do instruction rewriting for various other reasons, and the
>jump rewriting was just one small detail.
>But using 576 new lines (the diffstat for your patch 1/2 that adds the
>infrastructure to do the rewriting) in order to same just about
>exactly that many bytes in the binary - the effort just doesn't work
>out, imnsho.
> Linus

Sent from my mobile phone. Please excuse brevity and lack of formatting.
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