Subject: Re: i386 MP performance (generic.mp and generic almost same)
To: None <firstname.lastname@example.org>
From: Michael Lorenz <email@example.com>
Date: 11/11/2007 09:58:59
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On Nov 11, 2007, at 09:47, Paul Goyette wrote:
> On Sun, 11 Nov 2007, Steven M. Bellovin wrote:
>> Compilation is indeed CPU-bound; however, unless you've taken special
>> steps, it's a single process at a time. What you need to do is
>> '-j 2' when invoking build.sh, to run two processes simultaneously;
>> see /usr/src/BUILDING for details.
> In my experience, '-j 2' won't be enough to provide definitive
> results, since that seems to improve performance on uni-processor
> systems, too (though not by as much). On my AMD X2 systems I run
> builds with it set to '-j 4' and that seems to give the most benefit.
> But even on uni-processors '-j 2' will improve things since it
> gives a chance for a second job to run on the (only) CPU while the
> other one is waiting for I/O completion.
Same on my dual G4 - with -j2 both CPUs are running at about 60%
average, with -j4 both run at 100%.
Especially with sources over nfs the rule of thumb seems to be -j
(2*num_cpus) to avoid too much waiting.
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