Re: [PATCH v3 00/17] perf build: Reduce build time by nearly half

[Namhyung Kim <namhyung@kernel.org>]

On Thu, May 14, 2026 at 03:23:34PM -0700, Ian Rogers wrote:
> On Thu, May 14, 2026 at 3:06 PM Namhyung Kim <namhyung@kernel.org> wrote:
> >
> > On Thu, May 14, 2026 at 09:33:52AM -0700, Ian Rogers wrote:
> > > This patch series refactors Kbuild internals, BPF skeleton generation,
> > > Python AST pre-computation, and foundational tooling dependencies across
> > > the perf tool build system. By eliminating umbrella target synchronization
> > > barriers, decoupling static library prerequisites, parallelizing single-core
> > > script generators, and eradicating redundant feature checks, this series
> > > unlocks absolute theoretical peak multi-core concurrency during Kbuild startup.
> > >
> > > On a 28-core build workstation (make -j28 all from scratch), clean build
> > > latency improves by over 49%:
> > >
> > >   Before:
> > >     real    0m29.006s
> > >     user    2m46.019s
> > >     sys     0m30.610s
> > >
> > >   After:
> > >     real    0m14.782s
> > >     user    2m39.527s
> > >     sys     0m22.938s
> > >
> > > Saving 14.2 full seconds time per clean build. Furthermore, nothing to
> > > build incremental builds are improved by nearly 7x:
> > >
> > >   Before:
> > >     real    0m11.528s
> > >     user    0m9.633s
> > >     sys     0m6.965s
> > >
> > >   After:
> > >     real    0m1.729s
> > >     user    0m1.600s
> > >     sys     0m0.884s
> >
> > I've quickly checked it with latency profiling like below:
> >
> >   $ perf record --latency -- make -C tools/perf
> >
> >   $ perf report --latency -s comm
> >
> > The result looks like this.
> >
> > Before:
> >   #
> >   # Samples: 715K of event 'cpu/cycles/Pu'
> >   # Event count (approx.): 422452811481
> >   #
> >   #  Latency  Overhead  Command
> >   # ........  ........  ...............
> >   #
> >       45.28%    71.33%  cc1
> >       34.48%    16.92%  python3
> >       11.15%     2.21%  ld
> >        2.58%     1.51%  x86_64-linux-gn
> >        2.22%     0.99%  cc1plus
> >        0.71%     0.63%  sh
> >        0.69%     0.14%  llvm-config
> >        0.62%     0.56%  clang
> >        0.57%     4.40%  shellcheck
> >        0.44%     0.12%  perl
> >
> > After:
> >   #
> >   # Samples: 709K of event 'cpu/cycles/Pu'
> >   # Event count (approx.): 416654798495
> >   #
> >   #  Latency  Overhead  Command
> >   # ........  ........  ...............
> >   #
> >       64.99%    71.16%  cc1
> >       15.07%     1.81%  ld
> >        7.14%    17.59%  python3
> >        3.66%     1.53%  x86_64-linux-gn
> >        3.48%     0.75%  cc1plus
> >        1.11%     4.43%  shellcheck
> >        1.09%     0.74%  sh
> >        0.86%     0.59%  clang
> >        0.77%     0.12%  perl
> >        0.45%     0.23%  make
> >
> > Now I see a big drop in the latency from python.  And the llvm-config
> > doesn't show up in the top 10.
> 
> This looks good. What is "x86_64-linux-gn", and since we default off
> LIBPERL, why does perl show up in the commands?

I don't know exactly, but it seems we have some path to run perl during
the build even LIBPERL is off.  This is what `perf report --tasks` shows.

   3577076  3577076  3576925 |    sh
   3577077  3577077  3577076 |     make
   3577078  3577078  3577077 |      sh
   3577079  3577079  3577078 |       gcc
   3577081  3577081  3577079 |        cc1
   3577080  3577080  3577078 |       grep
   3577082  3577082  3577077 |      which
   3577083  3577083  3577077 |      sh
   3577084  3577084  3577083 |       perl
   3577085  3577085  3577077 |      sh
   3577086  3577086  3577085 |       perl
   3577087  3577087  3577086 |        pwd
   3577088  3577088  3577086 |        sh
   3577089  3577089  3577088 |         x86_64-linux-gn
   3577090  3577090  3577089 |          cc1

Thanks,
Namhyung