On Tue, 20 Oct 2026 18:34:21 GMT, Erik Joelsson <[email protected]> wrote:
> This is an interesting idea. I wasn't aware of this inefficiency in GNU Make. > The actual impact on complete build times is a bit more modest than you are > implying. With GNU Make 4.0 I'm seeing no practical improvement (tried clean > runs of make hotspot). With 4.4.1, which seems to be more sensitive to this > optimization, there seems to be some measurable improvement for a real clean > build. I don't have enough samples to give a reliable number however, but > it's in the single digit %. > > I also took the patch through COMPARE_BUILD runs on all our supported > platforms to make sure no important variable was lost. Those were successful. > > My concern is maintaining these lists of variables long term. It adds another > level of complexity on already quite complex makefiles. I think I can be ok > with it, but would like input from more build group people and OpenJDK > developers in general to gauge the actual impact of this change to see if > it's worth the trouble. My initial measurements were on Mac (M1 laptop). I ran more extensive testing on a cloud Linux VM. The reduced cpu time for the make processes is definitely real. Make 4.0 14.787 → 10.918 Make 4.4.1 21.659 → 10.750 Unfortunately, this doesn't translate to much actual performance gain across a real build (clean build of `make hotspot`): Make 4.0 463.650 → 463.077 Make 4.4.1 464.245 → 461.991 ------------- PR Comment: https://git.openjdk.org/jdk/pull/33454#issuecomment-6301230307
