On Fri, Apr 10, 2015 at 02:36:29PM -0700, Andrew Morton wrote: > On Thu, 9 Apr 2015 01:50:23 +0200 Andi Kleen <andi@xxxxxxxxxxxxxx> wrote: > > > > Head is spinning a bit. As this all appears to be shiny new > > > added-by-andi gcc functionality, it would be useful if we could have a > > > few more words describing what it's all about. Reordering of what with > > > respect to what and why and why is it bad. Why is gcc reordering > > > things anyway, and what's the downside of preventing this. Why is the > > > compiler reordering things rather than the linker. etc etc etc. > > > > Ok, let me try. > > That was super-useful, thanks. I slurped it into the changelog - > maybe one day it will provide material for Documentation/lto-stuff.txt. > > Big picture: do you have a feeling for how much benefit LTO will yield > in the kernel, if/when it's all completed? At least nothing of the stuff I usually run seems to be very kernel compiler dependent in performance. I think other people may benefit from it. Just looking at the code it is often a lot better. We've had great results in code size reduction for small systems though. I also found a range of bugs in the kernel which is good. The merge is also nearly finished, only a smaller number of patches left. There are some future technologies which could benefit from it too. There is still some compile time penalty, although it got a lot better with 5. I wouldn't expect developers to use it day-to-day, but it can be a good release mode. I think it's a good thing to have now, just for the benefits for shrinking kernels. -Andi -- ak@xxxxxxxxxxxxxxx -- Speaking for myself only. -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
