On Thu, Oct 07, 2021 at 02:51:15PM +0300, Andy Shevchenko wrote: > On Thu, Oct 7, 2021 at 1:34 PM Greg Kroah-Hartman > <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > On Thu, Oct 07, 2021 at 12:51:25PM +0300, Andy Shevchenko wrote: > > > The kernel.h is a set of something which is not related to each other > > > and often used in non-crossed compilation units, especially when drivers > > > need only one or two macro definitions from it. > > > > > > Here is the split of container_of(). The goals are the following: > > > - untwist the dependency hell a bit > > > - drop kernel.h inclusion where it's only used for container_of() > > > - speed up C preprocessing. > > > > > > People, like Greg KH and Miguel Ojeda, were asking about the latter. > > > Read below the methodology and test setup with outcome numbers. > > > > > > The methodology > > > =============== > > > The question here is how to measure in the more or less clean way > > > the C preprocessing time when building a project like Linux kernel. > > > To answer it, let's look around and see what tools do we have that > > > may help. Aha, here is ccache tool that seems quite plausible to > > > be used. Its core idea is to preprocess C file, count hash (MD4) > > > and compare to ones that are in the cache. If found, return the > > > object file, avoiding compilation stage. > > > > > > Taking into account the property of the ccache, configure and use > > > it in the below steps: > > > > > > 1. Configure kernel with allyesconfig > > > > > > 2. Make it with `make` to be sure that the cache is filled with > > > the latest data. I.o.w. warm up the cache. > > > > > > 3. Run `make -s` (silent mode to reduce the influence of > > > the unrelated things, like console output) 10 times and > > > measure 'real' time spent. > > > > > > 4. Repeat 1-3 for each patch or patch set to get data sets before > > > and after. > > > > > > When we get the raw data, calculating median will show us the number. > > > Comparing them before and after we will see the difference. > > > > > > The setup > > > ========= > > > I have used the Intel x86_64 server platform (see partial output of > > > `lscpu` below): > > > > > > $ lscpu > > > Architecture: x86_64 > > > CPU op-mode(s): 32-bit, 64-bit > > > Address sizes: 46 bits physical, 48 bits virtual > > > Byte Order: Little Endian > > > CPU(s): 88 > > > On-line CPU(s) list: 0-87 > > > Vendor ID: GenuineIntel > > > Model name: Intel(R) Xeon(R) CPU E5-2699 v4 @ 2.20GHz > > > CPU family: 6 > > > Model: 79 > > > Thread(s) per core: 2 > > > Core(s) per socket: 22 > > > Socket(s): 2 > > > Stepping: 1 > > > CPU max MHz: 3600.0000 > > > CPU min MHz: 1200.0000 > > > ... > > > Caches (sum of all): > > > L1d: 1.4 MiB (44 instances) > > > L1i: 1.4 MiB (44 instances) > > > L2: 11 MiB (44 instances) > > > L3: 110 MiB (2 instances) > > > NUMA: > > > NUMA node(s): 2 > > > NUMA node0 CPU(s): 0-21,44-65 > > > NUMA node1 CPU(s): 22-43,66-87 > > > Vulnerabilities: > > > Itlb multihit: KVM: Mitigation: Split huge pages > > > L1tf: Mitigation; PTE Inversion; VMX conditional cache flushes, SMT vulnerable > > > Mds: Mitigation; Clear CPU buffers; SMT vulnerable > > > Meltdown: Mitigation; PTI > > > Spec store bypass: Mitigation; Speculative Store Bypass disabled via prctl and seccomp > > > Spectre v1: Mitigation; usercopy/swapgs barriers and __user pointer sanitization > > > Spectre v2: Mitigation; Full generic retpoline, IBPB conditional, IBRS_FW, STIBP conditional, RSB filling > > > Tsx async abort: Mitigation; Clear CPU buffers; SMT vulnerable > > > > > > With the following GCC: > > > > > > $ gcc --version > > > gcc (Debian 10.3.0-11) 10.3.0 > > > > > > The commands I have run during the measurement were: > > > > > > rm -rf $O > > > make O=$O allyesconfig > > > time make O=$O -s -j64 # this step has been measured > > > > > > The raw data and median > > > ======================= > > > Before patch 2 (yes, I have measured the only patch 2 effect) in the series > > > (the data is sorted by time): > > > > > > real 2m8.794s > > > real 2m11.183s > > > real 2m11.235s > > > real 2m11.639s > > > real 2m11.960s > > > real 2m12.014s > > > real 2m12.609s > > > real 2m13.177s > > > real 2m13.462s > > > real 2m19.132s > > > > > > After patch 2 has been applied: > > > > > > real 2m8.536s > > > real 2m8.776s > > > real 2m9.071s > > > real 2m9.459s > > > real 2m9.531s > > > real 2m9.610s > > > real 2m10.356s > > > real 2m10.430s > > > real 2m11.117s > > > real 2m11.885s > > > > > > Median values are: > > > 131.987s before > > > 129.571s after > > > > > > We see the steady speedup as of 1.83%. > > > > You do know about kcbench: > > https://gitlab.com/knurd42/kcbench.git > > > > Try running that to make it such that we know how it was tested :) > > I'll try it. > > 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... thanks, greg k-h
