linux-kernel - Re: make -jN (n>1) ineffective in 4.2.0-rc on AMD Phenom

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Message-ID: <20150715122800.GA14373@milliways>
Date:	Wed, 15 Jul 2015 13:28:00 +0100
From:	Ken Moffat <zarniwhoop@...world.com>
To:	Jeff Epler <jepler@...ythonic.net>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: make -jN (n>1) ineffective in 4.2.0-rc on AMD Phenom

On Tue, Jul 14, 2015 at 09:23:31PM -0500, Jeff Epler wrote:
> GNU Make 4.1 has a problem that causes it to be unable to use the
> desired level of parallelism.  Two people have reported that reverting a
> commit which changes from fork to vfork "fixes" it. (i'm one of them,
> unfortunately posting as anonymous in the tracker).
> 
> Hoewver, if you are also seeing the linux kernel version as relevant to
> producing the problem, that's quite interesting, and the underlying
> cause may be different.  We reproduced the problem on a range of older
> kernels, from 3.2 to 3.18.
> 
> http://savannah.gnu.org/bugs/?44555
> 
> Jeff

Thanks, but I think this is a different problem, I was probably not
clear : I specify make -j4 and make does indeed run 4 jobs, but it
is only getting the equivalent of 1 CPU instead of 4.  It is
running 4 jobs, but on the equivalent of 1  processor (so this takes
much longer than -j1).

The reason I think it is a different problem is that I upgraded to
make-4.1 in November and everything has been fine until now.

With 'top' from procps-ng-3.3.10 the display can show how active
each CPU is (indeed, I think that is the default) - on earlier
versions of 'top' I think that the output was very different.

ĸen
-- 
This one goes up to eleven!
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