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From: Richard Purdie <richard.purdie@linuxfoundation.org>
To: "Tian, Kevin" <kevin.tian@intel.com>
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Date: Mon, 20 Dec 2010 13:09:11 +0000
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Cc: poky <poky@yoctoproject.org>
Subject: Re: Performance regression in bitbake and exec() vs fork()
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On Sat, 2010-12-18 at 08:46 +0800, Tian, Kevin wrote:
> >Mark has some numbers which don't quiet add up with improvements in read
> >and sys but an increase in user too, we're still looking to understand
> >them. I'd like to give the autobuilder a pass over these changes when we
> >have the opportunity and see what that real world performance looks
> >like.
> >
> >Its likely that the speedups will be greatest on machines with small
> >numbers of cores which are primarily cpu bound. The benefits will
> >decrease on disk IO bound systems with large number of cores.
> >
> 
> any elaboration on this difference?

The exec overhead occurs in the bitbake worker processes. The more
threads that are available, the more work happens in parallel and the
less this overhead can be "seen" in the overall time profile.

Secondly, the fork overhead is 'CPU' based. If the overall build time is
IO bound and not CPU bound, the less you'll see this overhead on a time
profile.

Cheers,

Richard.