Re: build performance: bb-matrix on 4-core (BB_NUMBER_THREADS and PARALLEL_MAKE optimization)

[Darren Hart <dvhart@linux.intel.com>]

On 07/08/2011 01:44 PM, Robert Berger wrote:
> Darren/Richard,
> 
> Maybe we could instead of hacking hard coded default values (or nothing)
> into the config file default to something like this:
> 
> somehow get the number of CPUs:
> 
> CPUS=$(grep ^processor /proc/cpuinfo | wc -l)
> echo CPUS=${CPUS}
> 
> or
> 
> CPUS=`getconf _NPROCESSORS_ONLN`
> echo CPUS_UBUNTU=${CPUS_UBUNTU}
> 
> (don't know if the second one will also work with other distros than Ubuntu)
> 
> Do some calculation which magic number for BB_NUMBER_THREADS and
> PARALLEL_MAKE to use:
> 
> e.g. what was suggested: BB=2*NR_CORES PM=1.5*NR_CORES

My concern with this is that on larger machines I'm seeing very
different optimal multipliers. On my 12 core with a RAID 0 build array,
the ideal setting seems to be BB=12 PM=12.

Until we can better characterize the ideal settings, I think we are
better off documenting what works for specific systems. Now perhaps we
need to do something that caps the number, but that is sure to be wrong
in short order as well.

As your signature suggests, the solution to this isn't likely to be
simple ;-)

--
Darren

> 
> Regards,
> 
> Robert
> ...For every complex problem there is a solution which is simple, neat
> and wrong. -- H.L. Mencken
> 
> My public pgp key is available at:
> http://pgp.mit.edu:11371/pks/lookup?op=get&search=0x90320BF1
> 
> 
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-- 
Darren Hart
Intel Open Source Technology Center
Yocto Project - Linux Kernel