On 2016.10.27 at 16:53 +0100, Sven C. Dack wrote: > Hello, > > I've been installing private copies of gcc for a while now, but only > recently did I notice that my distro's gcc (Debian testing) is doing much > better when comparing compile times than any of my copies. For instance does > it take 230s for my copy to compile a linux kernel, but only 163s for my > distro's gcc, which is almost a minute in difference for something that > doesn't take more than 3-4 minutes to compile. > > What makes this noteworthy for me is that I've compiled my copy with > profiledbootstrap and LTO enabled and also optimized it for my CPU, whereas > the distro's compiler won't have been optimized quite that much, but yet is > it so much faster in speed. I don't know how exactly my distro's gcc has > been set up, because the Debian build rules are rather complex and include > their own set of patches. So I thought I start with asking here first. > > What is that can make such a huge difference in compile speed for two copies > of gcc, both version 6.2, using the same options, on the same source? Or are > any of the configure options know to have a huge impact on the resulting > compiler's speed? Interesting. But without knowing the exact configuration and build options it is hard to tell what is going on. It is known however that a PGO/LTO bootstrapped compiler is slower that a pure PGO bootstrapped one on X86. However the difference is much lower that what you observe (low single digit percentage, not your measured 30%). -- Markus
