On Sat, Jul 01, 2017 at 02:28:44PM -0700, Christopher Li wrote: > On Sat, Jul 1, 2017 at 2:02 PM, Luc Van Oostenryck > <luc.vanoostenryck@xxxxxxxxx> wrote: > > > > Oh, I have no reason to believe that this variance had anything > > to do with the build system. Sure kbuild have some overhead (not > > much though) but it should be as deterministic as the rest. > > I should correct that I don't know how consistent is kbuild. > For me kbuild has very noticeable overhead on incremental build > compare to my script: > > One job: > $ time make ... > real 2m22.493s > user 1m44.339s > sys 0m35.836s > > Change that to 12 jobs: > $ time make -j12 ... > real 0m44.660s > user 2m10.570s > sys 0m45.502s > > > With my make script: > $ time make -f $PWD/linux-checker.make -C ../linux name=master > real 0m4.168s > user 0m4.008s > sys 0m0.143s > > $ time make -j12 -f $PWD/linux-checker.make -C ../linux name=master > real 0m4.206s > user 0m4.106s > sys 0m0.181s Yes, I did some simple 'make vmlinux' on an allyesconfig kernel which was already compiled and I was surprised by the time it took (all times in seconds, followed between the parenthesis by standard deviation, relative standard deviation and the standard error (of the mean): nbr measures: 12 real: 71.90 (1.50 = 2.09% ~ 0.67) user: 57.19 (1.19 = 2.08% ~ 0.53) sys: 10.30 (0.36 = 3.52% ~ 0.16) But the variance is not much, about the same as full compile or full check by sparse (see here under). > You don't have to do the test. I am fine with this change. I am just > curious with > the numbers myself. I'm interested myself in some good numbers. The result for an allyesconfig kernel without using kbuild: NR = 29, nbr measures: 12 real: 1080.44 (2.62 = 0.24% ~ 0.76) user: 818.06 (2.27 = 0.28% ~ 0.66) sys: 227.18 (1.12 = 0.49% ~ 0.32) NR = 13, nbr measures: 20 real: 1064.25 (1.65 = 0.15% ~ 0.37) user: 816.35 (1.29 = 0.16% ~ 0.29) sys: 213.33 (0.90 = 0.42% ~ 0.20) NR = 05, nbr measures: 11 real: 1058.52 (2.57 = 0.24% ~ 0.78) user: 817.17 (2.34 = 0.29% ~ 0.70) sys: 207.12 (0.95 = 0.46% ~ 0.29) For the speedup, this gives us: 1) using NR=13 instead of 29: real: 16.19 (1.50%) user: 1.71 (0.21%) sys: 13.85 (6.10%) 1) using NR=5 instead of 29: real: 21.92 (2.03%) user: 0.89 (0.11%) sys: 20.06 (8.83%) So, the speedup on the whole kernel is real but modest: * 1.5-2.0% on real time, * the gain in user time is negligible and smaller than the std dev. -> cache effect is very small or inexisting or is compensated by some extra work due to the use of more list blocks. * the speedup in system time is appreciable though: 6-8% I have done some others tests with NR = 7, 9, ... They are not much interesting, giving times similar but a bit higher than for NR = 13 (but for NR = 9). The differences are anyway quite small. -- Luc -- To unsubscribe from this list: send the line "unsubscribe linux-sparse" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
