On 08/07/2013 03:22 PM, Linus Torvalds wrote: > On Wed, Aug 7, 2013 at 10:54 AM, Steven Rostedt <rost...@goodmis.org> wrote: >> 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
The whole point of the thread started with wanting to move the default 'disabled' branch further out-of-line. We could get there with better compiler support for the 'cold' label attribute. Thus, in theory the whole 2-byte jmp is just an intermediate step. (Yeah, I know that support doesn't seem to be happening anytime soon...) Thanks, -Jason -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
