* Douglas Anderson <dianders@xxxxxxxxxxxx> wrote: > 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. Very impressive! > [...] ...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. I don't think that's a worst case: incremental builds are very commonly used during kernel development and kernel testing. (I'd even argue that the performnace of incremental builds is one of the most important features of a build system.) That it's called twice in the Chrome OS build system does not change the proportion of the speedup. > 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. This is a huge deal! FWIIW I have tested your patches and they work fine here. Here's the before/after performance testing of various styles of build times of the scheduler. First the true worst case is a full rebuild: [ before ] triton:~/tip> perf stat --null --repeat 3 --pre "make clean 2>/dev/null 2>&1" make kernel/sched/ >/dev/null Performance counter stats for 'make kernel/sched/' (3 runs): 4.693974827 seconds time elapsed ( +- 0.05% ) [ after ] triton:~/tip> perf stat --null --repeat 3 --pre "make clean 2>/dev/null 2>&1" make kernel/sched/ >/dev/null Performance counter stats for 'make kernel/sched/' (3 runs): 4.391769610 seconds time elapsed ( +- 0.21% ) Still a ~6% speedup which is nice to have. Then the best case, a fully cached rebuild of a specific subsystem - which I personally do all the time when I don't remember whether I already built the kernel or not: [ before ] triton:~/tip> taskset 1 perf stat --null --pre "sync" --repeat 10 make kernel/sched/ >/dev/null Performance counter stats for 'make kernel/sched/' (10 runs): 0.439517157 seconds time elapsed ( +- 0.14% ) [ after ] triton:~/tip> taskset 1 perf stat --null --pre "sync" --repeat 10 make kernel/sched/ >/dev/null Performance counter stats for 'make kernel/sched/' (10 runs): 0.148483807 seconds time elapsed ( +- 0.57% ) A 300% speedup on my system! So I wholeheartedly endorse the whole concept of caching build environment invariants: Tested-by: Ingo Molnar <mingo@xxxxxxxxxx> Thanks, Ingo -- 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