On Tue, Jan 04, 2022 at 11:47:30AM +0100, Ingo Molnar wrote: > > > With the fast-headers kernel that's down to ~36,000 lines of code, > > > almost a factor of 3 reduction: > > > > > > # fast-headers-v1: > > > kepler:~/mingo.tip.git> wc -l kernel/pid.i > > > 35941 kernel/pid.i > > > > Coming from someone who often has to reduce a preprocessed kernel source > > file with creduce/cvise to report compiler bugs, this will be a very > > welcomed change, as those tools will have to do less work, and I can get > > my reports done faster. > > That's nice, didn't think of that side effect. > > Could you perhaps measure this too, to see how much of a benefit it is? As it turns out, I got an opportunity to measure this sooner rather than later [1]. Using cvise [2] with an identical set of toolchains and interestingness test [3], reducing net/core/skbuff.c took significantly less time with the version from the fast-headers tree. v5.16-rc8: $ wc -l skbuff.i 105135 skbuff.i $ time cvise test.fish skbuff.i ... ________________________________________________________ Executed in 114.02 mins fish external usr time 1180.43 mins 69.29 millis 1180.43 mins sys time 229.80 mins 248.11 millis 229.79 mins fast-headers: $ wc -l skbuff.i 78765 skbuff.i $ time cvise test.fish skbuff.i ... ________________________________________________________ Executed in 47.38 mins fish external usr time 620.17 mins 32.78 millis 620.17 mins sys time 123.70 mins 122.38 millis 123.70 mins I was not expecting that much of a difference but it somewhat makes sense, as the tool spends less time eliminated unused code and the compiler invocations will be incrementally quicker as the input becomes smaller. [1]: https://github.com/ClangBuiltLinux/linux/issues/1563 [2]: https://github.com/marxin/cvise [3]: https://github.com/nathanchance/creduce-files/tree/61056fd763ae3bfb53ff0ae4c1d95550c7c0a5b7/cbl-1563 Cheers, Nathan
