Re: [PATCH v2 0/4] kernel.h further split

On Thu, Oct 07, 2021 at 05:47:31PM +0300, Andy Shevchenko wrote:

On Thu, Oct 07, 2021 at 03:59:08PM +0200, Greg Kroah-Hartman wrote:

quoted

On Thu, Oct 07, 2021 at 02:51:15PM +0300, Andy Shevchenko wrote:

quoted

On Thu, Oct 7, 2021 at 1:34 PM Greg Kroah-Hartman
[off-list ref] wrote:

...

quoted

quoted

Meanwhile, Thorsten, can you have a look at my approach and tell if it
makes sense?

No, do not use ccache when trying to benchmark the speed of kernel
builds, that tests the speed of your disk subsystem...

First rule of the measurement is to be sure WHAT we are measuring.
And I'm pretty much explained WHAT and HOW. On the other hand, the
kcbench can't answer to the question about C preprocessing speed
without help of ccache or something similar.

Measuring complete build is exactly not what we want because of
O(compilation) vs. o(C preprocessing) meaning that any fluctuation
in the former makes silly to measure anything from the latter.

You see, my theory is proved by practical experiment:

$ kcbench -i 3 -j 64 -o $O -s $PWD --no-download -m
Processor:           Intel(R) Xeon(R) CPU E5-2699 v4 @ 2.20GHz [88 CPUs]
Cpufreq; Memory:     powersave [intel_pstate]; 128823 MiB
Linux running:       5.6.0-2-amd64 [x86_64]
Compiler:            gcc (Debian 10.3.0-11) 10.3.0
Linux compiled:      5.15.0-rc4
Config; Environment: allmodconfig; CCACHE_DISABLE="1"
Build command:       make vmlinux modules
Filling caches:      This might take a while... Done
Run 1 (-j 64):       464.07 seconds / 7.76 kernels/hour [P:6001%]
Run 2 (-j 64):       464.64 seconds / 7.75 kernels/hour [P:6000%]
Run 3 (-j 64):       486.41 seconds / 7.40 kernels/hour [P:5727%]

$ kcbench -i 3 -j 64 -o $O -s $PWD --no-download -m
Processor:           Intel(R) Xeon(R) CPU E5-2699 v4 @ 2.20GHz [88 CPUs]
Cpufreq; Memory:     powersave [intel_pstate]; 128823 MiB
Linux running:       5.6.0-2-amd64 [x86_64]
Compiler:            gcc (Debian 10.3.0-11) 10.3.0
Linux compiled:      5.15.0-rc4
Config; Environment: allmodconfig; CCACHE_DISABLE="1"
Build command:       make vmlinux modules
Filling caches:      This might take a while... Done
Run 1 (-j 64):       462.32 seconds / 7.79 kernels/hour [P:6009%]
Run 2 (-j 64):       462.33 seconds / 7.79 kernels/hour [P:6006%]
Run 3 (-j 64):       465.45 seconds / 7.73 kernels/hour [P:5999%]

In [41]: numpy.median(y1)
Out[41]: 464.64

In [42]: numpy.median(y2)
Out[42]: 462.33

Speedup: +0.5%

Good, you measured what actually matters here, the real compilation of
the code, not just the pre-processing of it.

thanks,

greg k-h