Re: PCH build times (Re: new gerrit-builds & unit tests ...)

Hi,

On Fri, Apr 05, 2013 at 11:01:24PM +0200, Lubos Lunak wrote:
> On Friday 05 of April 2013, Bjoern Michaelsen wrote:
> > On Fri, Apr 05, 2013 at 11:16:06AM -0500, Norbert Thiebaud wrote:
> > > I enabled pch because it was claimed to speed up things... I have not
> > > benchmark that claim.
> >
> > I would benchmark that, at least in the old days the results of PCH where
> > really mixed:
> >
> > http://wiki.openoffice.org/wiki/Build_Environment_Effort/Performance
> >
> > and only reliably gave an advantage on incremental builds. OTOH, generating
> > the PCH for a library was a singlethreaded bottleneck in the old build
> > system and isnt anymore in gbuild, when doing a toplevel make, so this
> > might be mitigated.
> >
> > Anyway, worth a benchmark IMHO.
>
>  make Library_sw
>
> PCH: 7:01
> non-PCH: 20:31

Good! That means its roughly the same and with toplevel make it should actually
be better with gbuild now, as it doesnt do:

- finish one module
- generate PCH single threaded (here gbuild will be happily build stuff from
  other modules along)
- only then, start building objects

sw had a well-maintained PCH most of the time, while sc did not -- at least
that was the assumption to explain why sw was helped by PCH while sc wasnt.
Just out of curiousity, what are the numbers for sc now, if you have them at
hand?

Best,

Bjoern