Re: make -j with j <= 4 seems to only load a single CPU core

["Jesper Juhl" <jesper.juhl@gmail.com>]

On 2/21/06, Paul Fulghum <paulkf@microgate.com> wrote:
> On Tue, 2006-02-21 at 22:10 +0100, Jesper Juhl wrote:
>
> > I should probably mention that the kernel I'm currently running and
> > observing this behaviour with is 2.6.16-rc4-mm1.
> ...
> > > I find this quite strange since anything from 'make -j 2' and up
> > > should be able to keep both cores resonably busy, but there seems to
> > > be a huge difference between j <= 4 and j > 4.
>
> I've seen the same thing (on Athlon 64x2 64 bit)
> but was not sure if it was a problem.
>
> The break point for me seems to be between -j 2 and -j 3
> -j 2 = serialized (or the appearance of)
> -j 3 = both cores mostly busy
>
> I'm pretty sure with an earlier 2.6 kernel source (but same environment)
> I did not see this. I'll start back tracking to earlier kernels
> to see if I can identify when this started.
>

I know positively that I've seen this with previous 2.6.16-<something>
kernels, but not sure which ones exactely. I just dismissed it as
something that would probably be fixed soon and then today when I
build a few test kernels I noticed it again and thought "ohh, so it
didn't get fixed, better report it".

I don't recall seeing it with 2.6.15 and earlier kernels, but I'm not
at all sure - especially since I only got this Athlon X2 box recently
and the first kernels I ever ran on it were 2.6.15-<something>.

--
Jesper Juhl <jesper.juhl@gmail.com>
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