distcc only builds locally when using rpmbuild

[Sam Varshavchik]

Suvayu Ali writes:

> Hi Sam,
>
> On Sun, May 31, 2015 at 08:05:44PM -0400, Sam Varshavchik wrote:
> > Suvayu Ali writes:
> > >
> > >How does rpmbulid decide how many threads to run?  I think it looks at
> > >the local machine and decides.  I also recall some variable called
> > >RPMBUILD_NCPU or something like that.  That would explain why it only
> > >uses as many threads as the local machine can handle.
> > >
> > >Hope this helps,
> >
> > Sadly, no it doesn't.  As I wrote above:
> >
> > >> >> >> ps shows the maximum number of "/usr/bin/distcc /usr/bin/g++
> > >[options]"
> > >> >> >> processes running locally,
> >
> > rpmbuild uses the _smp_mflags macro to pass the -j parameter to make, and I
> > have it correctly configured to kick off ten parallel processes, to match
> > the maximum number of ten processes distcc is configured (4 local, 6
> > remote). Yet, despite the fact that a manual build distributes the compiles
> > correctly, with rpmbuild distcc throttles the number of concurrent parallel
> > jobs that it kicks off to four, and runs them locally.
>
> I think you misunderstood me, I wasn't clear either.  I saw you set
> _smp_mflags, what I mean is rpmbuild still does some magic underneath.
> I.e. after you have set that flag, afaik, rpmbuild will fiddle with the
> value and pass an "appropriate" -j<n> flag to Make in the regular case.
> It makes this choice based on how many threads it can run locally.  At
> least that's what I think it does.
>
> Okay I did some digging.  This is what rpmbuild does with _smp_mflags
> (output from rpmbuild --showrc).
>
> -14: _smp_mflags        %([ -z "$RPM_BUILD_NCPUS" ] \
>         && RPM_BUILD_NCPUS="`/usr/bin/getconf _NPROCESSORS_ONLN`"; \
>         ncpus_max=%{?_smp_ncpus_max}; \
>         if [ -n "$ncpus_max" ] && [ "$ncpus_max" -gt 0 ] &&  
> [ "$RPM_BUILD_NCPUS" -gt "$ncpus_max" ]; then RPM_BUILD_NCPUS="$ncpus_max";  
> fi; \
>         if [ "$RPM_BUILD_NCPUS" -gt 1 ]; then echo "-j$RPM_BUILD_NCPUS"; fi)
> -14: _smp_ncpus_max     16
>
> I don't have the time to check the above snippet, maybe you can take a
> look?  Hope this time we follow each other.  If this doesn't help, I'm
> out of ideas :-(.

That's nice, except, as I mentioned, I override all of this nonsense in  
my .rpmmacros, and replace it with a simple

%_smp_mflags	 -j 10

Once again: the correct number of distcc processes get started. But they  
throttle each other, and only four, at a time, kick off a compile on  
localhost, the configured distcc max job setting for localhosts, with the  
others waiting until the earlier ones finish, before starting the real g++.  
distcc does that on its own. It's configured for a maximum number of  
concurrent jobs in /etc/distcc/hosts, and if more than that are started,  
they throttle each other.

I believe I already explained this, but I'm having some apparent difficulty  
carrying across that, for some reason, distcc ends up ignoring everything  
but the localhost setting, in /etc/distcc/hosts, when it's started from  
rpmbuild. That's where the problem is. Obviously rpmbuild has something to  
do with it, but it's not the direct setting. rpmbuild's %_smp_mflags is  
configured correctly, and it's doing it's job of kicking off make -j 10, as  
it should be.

I was hoping that someone came across this glitch before, and knew the root  
cause. I guess not, and I suppose I'll have to strace the whole thing, and  
see if that uncovers any clues.

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