[libvirt PATCH 342/351] meson: add syntax-check

[Peter Krempa]

On Tue, Jul 28, 2020 at 15:08:11 +0100, Daniel Berrange wrote:
> On Tue, Jul 28, 2020 at 04:04:39PM +0200, Pavel Hrdina wrote:
> > On Tue, Jul 28, 2020 at 03:48:29PM +0200, Peter Krempa wrote:
> > > On Thu, Jul 16, 2020 at 11:59:38 +0200, Pavel Hrdina wrote:
> > > > Signed-off-by: Pavel Hrdina <phrdina at redhat.com>
> > > > ---
> > > >  build-aux/Makefile.in                         |  9 +++
> > > >  .../Makefile.nonreentrant                     |  0
> > > >  build-aux/meson.build                         | 30 +++++++++
> > > >  build-aux/syntax-check.mk                     | 62 +++++++++----------
> > > >  meson.build                                   |  2 +
> > > >  5 files changed, 72 insertions(+), 31 deletions(-)
> > > >  create mode 100644 build-aux/Makefile.in
> > > >  rename Makefile.nonreentrant => build-aux/Makefile.nonreentrant (100%)
> > > >  create mode 100644 build-aux/meson.build
> > > 
> > > [...]
> > > 
> > > > +make_prog = find_program('make')
> > > > +
> > > > +# There is no way how to pass value to -j using run_target so let's use
> > > > +# it without any value to run all tests in parallel.
> > > > +run_target(
> > > > +  'syntax-check',
> > > > +  command: [
> > > > +    make_prog, '-C', meson.current_build_dir(), '-j', 'syntax-check',
> > > > +  ],
> > > 
> > > While I do run syntax check with unlimited '-j'. I don't think it's
> > > entirely cool to impose that on everybody. Specifically overcommiting
> > > the system is not cool. Since meson is automagically scaling can't we
> > > use the meson-detected cpu number here?
> > 
> > Unfortunately no, that was the first thing I was trying to figure out
> > by going through meson code as well. It's not ideal I know.
> > 
> > Other options are to not use -j at all which is no-go or we can add some
> > code to detect the available number of CPUs. But again it would not
> > reflect the fact if user runs 'ninja -j N'.
> 
> In libosinfo we put "syntax-check" as part of the unit tests, rather
> than as a separate meson target. With that you don't need to pass
> -j to syntax-check, because other unit tests are running in parallel
> already, and chances are syntax-check will finish first even when
> serialized.

Unfortunately it's not even close.

Serialized syntax-check:
real	0m22.139s
user	0m24.209s
sys	0m6.788s

test suite:
real	0m4.833s
user	0m12.408s
sys	0m3.918s

syntax-check with -j == ncpus: (24 thread box)

real	0m2.099s
user	0m28.558s
sys	0m7.739s


As said, I'm a big fan of -jncpus or -j. so I really want to keep it
especially given the data above, but on the other hand I don't want to
set the CI boxes on fire.