This two-patch series attempts to speed incremental builds of the kernel up by a bit. How much of a speedup you get depends a lot on your environment, specifically the speed of your workstation and how fast it takes to invoke the compiler. In the Chrome OS build environment you get a really big win. For an incremental build (via emerge) I measured a speedup from ~1 minute to ~35 seconds. ...but Chrome OS calls the compiler through a number of wrapper scripts and also calls the kernel make at least twice for an emerge (during compile stage and install stage), so it's a bit of a worst case. Perhaps a more realistic measure of the speedup others might see is running "time make help > /dev/null" outside of the Chrome OS build environment on my system. When I do this I see that it took more than 1.0 seconds before and less than 0.2 seconds after. So presumably this has the ability to shave ~0.8 seconds off an incremental build for most folks out there. While 0.8 seconds savings isn't huge, it does make incremental builds feel a lot snappier. Caveats from v1 still copied here, though with Masahiro Yamada's suggestions from v1 this is starting to feel a little more baked and I've even dropped the RFC from it (though extra testing still appreciated): Please note that I make no illusions of being a Makefile expert nor do I have any belief that I fully understand the Linux kernel build system. Please take this patch series as the start of a discussion about whether others feel like this type of speedup is worthwhile and how to best accomplish it. Specific things to note: - I'm happy to paint the bikeshed any color that maintainers want. If you'd like the cache named differently, in a slightly different format, or you want me to adjust the spacing / names of Makefile stuff then please just let me know. - If this is totally the wrong approach and you have a better idea then let me know. If you want something that's super complicated to explain then feel free to post a replacement patch and I'm happy to test. - This patch definitely needs extra testing. I've tested it on a very limited build environment and it seems to be working fine, but I could believe that with some weird compiler options or on certain architectures you might need some extra escaping here and there. Changes in v2: - Abstract at a different level (like shell-cached) per Masahiro Yamada - Include ld-version, which I missed the first time Douglas Anderson (2): kbuild: Add a cache for generated variables kbuild: Cache a few more calls to the compiler Documentation/kbuild/makefiles.txt | 21 +++++++++ Makefile | 4 +- scripts/Kbuild.include | 90 ++++++++++++++++++++++++++++++++------ 3 files changed, 99 insertions(+), 16 deletions(-) -- 2.14.2.920.gcf0c67979c-goog -- 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
