Messages in this thread | | | Date | Tue, 21 Feb 2006 22:59:33 +0100 | From | "Jesper Juhl" <> | Subject | Re: make -j with j <= 4 seems to only load a single CPU core |
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On 2/21/06, linux-os (Dick Johnson) <linux-os@analogic.com> wrote: > > On Tue, 21 Feb 2006, Jesper Juhl wrote: > > > 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> > > Don't top-post http://www.catb.org/~esr/jargon/html/T/top-post.html > > Plain text mails only, please http://www.expita.com/nomime.html > > Could it be, simply, that you are now I/O bound with nothing > for these CPUs to do in user-space, being busy handling the > kernel I/O? >
I doubt it. If that was the case then I should be I/O bound with 'make -j 4' and even more so with 'make -j 5'. But what I'm seeing is that with 'make -j 4' (and less) only ~50% of my CPU resources are being used but with 'make -j 5' I get close to 100% CPU utilization.
-- Jesper Juhl <jesper.juhl@gmail.com> Don't top-post http://www.catb.org/~esr/jargon/html/T/top-post.html Plain text mails only, please http://www.expita.com/nomime.html - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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