Re: [PATCH] kbuild: try readelf first in gen_symversions

["Wentao Guan" <guanwentao@uniontech.com>]

Hello,

> This should probably be CONFIG_LTO_CLANG with flipped branches but...
Right!

> '-m1' appears to get us 50% (12s) of the speed up of 'readelf' (24s) in
> your environment while sticking with 'nm'. I would be more inclined to
> take that change since it is small and correct, rather than switching on
> NM or READELF, as I don't think it is worth the additional complexity.
> FWIW, on one of my test machines with 8 cores and 16 threads, the
> difference is much less noticeable. I think that is going to be in line
>  with most developer and build farm hardware, rather than a 2C/4T machine
> like you mention in the initial commit message.
Sorry, it seems my cloud servies provider cause my results  up and down:(,
also maybe first compile time not stable, so I tested in a 20 cores/28 threads 
bare metal envirment , here is the result:

Intel(R) Core(TM) i7-14700HX + 32GB + NVMe ssd
gcc version 12.3.0 binutils 2.46
clang version 18.1.7
source kernel tag v7.0

summary:
1. still benifit from nm to readelf in 20core/28threads
(I think there more costs in libbfd in nm, show high cost down in sys time,
I guess it cause more memory acces bottle neck to effect overall compile process)
but seems no these different when change llvm-18-nm to llvm-18-readelf
2. -m1 seems no expect effect...

test scripts:
https://gist.github.com/opsiff/832baa9a6986343dddbe530fbee57f52

Makefile.build-nm-m1  : 'grep -q' -> 'grep -m1 -q'
Makefile.build-orig : orig Makefile.build
Makefile.build-readelf : 'NM' -> 'READELF -sW'
Makefile.build-readelf-m1: 'NM' -> 'READELF -sW' , 'grep -q' -> 'grep -m1 -q'

full result:
1. run x86_64_defconfig + modversions x3(base)
        if $(NM) $@ 2>/dev/null | grep -q ' __export_symbol_'; then             \
real    2m2.876s   real    2m2.578s   real    2m2.262s
user    42m15.871s   user    42m35.250s   user    42m33.679s
sys     5m52.904s  sys     5m52.478s   sys     5m49.009s

2. if $(READELF) -sW $@ 2>/dev/null | grep -q  __export_symbol_; then
real    1m54.931s   real    1m55.192s   real    1m55.207s
user    41m4.162s   user    41m7.754s   user    41m5.791s
sys     4m8.422s   sys     4m8.431s   sys     4m9.219s

3. if $(NM) $@ 2>/dev/null | grep -m1 -q  __export_symbol_; then    \

real    2m1.865s   real    2m1.866s   real    2m2.108s
user    42m32.891s   user    42m35.047s  user    42m33.834s
sys     5m48.045s  sys     5m47.700s   sys     5m48.200s

4. if $(READELF) -sW $@ 2>/dev/null | grep -m1 -q ' __export_symbol_'; then    \

real    1m55.386s   real    1m56.528s   real    1m55.489s
user    41m6.156s   user    41m12.321s   user    41m10.545s
sys     4m10.093s   sys     4m9.838s   sys     4m9.367s

5. LLVM run x86_64_defconfig + modversions x3(base)
        if $(NM) $@ 2>/dev/null | grep -q ' __export_symbol_'; then             \

real    2m35.758s   real    2m32.696s   real    2m32.127s
user    58m2.416s   user    57m55.030s   user    57m54.806s
sys     4m20.735s   sys     4m18.473s   sys     4m18.090s

6. LLVM if $(READELF) -sW $@ 2>/dev/null | grep -q ' __export_symbol_'; then        \

real    2m32.448s   real    2m32.419s   real    2m32.509s
user    57m57.262s   user    57m53.001s   user    57m48.842s
sys     4m20.508s   sys     4m20.693s   sys     4m20.490s

7. LLVM  if $(NM) $@ 2>/dev/null | grep -m1 -q ' __export_symbol_'; then         \

real    2m32.003s  real    2m31.900s   real    2m32.276s
user    57m45.786s   user    57m46.982s   user    57m49.907s
sys     4m18.184s   sys     4m17.923s   sys     4m18.354s


8. LLVM if $(READELF) -sW $@ 2>/dev/null | grep -m1 -q ' __export_symbol_'; then    \

real    2m33.365s   real    2m32.186s  real    2m32.114s
user    57m49.533s   user    57m47.865s   user    57m46.591s
sys     4m19.809s  sys     4m20.652s   sys     4m19.954s

9. LLVM LTO_THIN run x86_64_defconfig + modversions x3(base)
        if $(NM) $@ 2>/dev/null | grep -q ' __export_symbol_'; then             \

real    3m59.411s    real    3m55.945s   real    3m56.557s
user    59m38.877s    user    59m20.007s   user    59m19.009s
sys     4m21.582s   sys     4m22.313s   sys     4m23.793s

10. LLVM LTO_THIN  if $(NM) $@ 2>/dev/null | grep -m1 -q ' __export_symbol_'; then         \

real    3m55.722s   real    3m56.641s   real    3m57.979s
user    59m21.865s   user    59m25.634s   user    59m20.872s
sys     4m21.303s   sys     4m24.174s   sys     4m22.695s

Full log:
https://gist.github.com/opsiff/1cd7e0a0553c8416dd13a7e92590a440

If you have any other ideas, i will happly to test them,
i will try to use llvm-nm instead of nm to test.

BRs
Wentao Guan