Re: [uml-user] Very low performances on UML

[Blaisorblade <bla...@ya...>]

On Saturday 20 January 2007 17:39, Flavio wrote:
> 2007/1/20, Blaisorblade <bla...@ya...>:
> > I.e. a SMP processor obviously, right?
>
> That's right!
>
> > UML does not support SMP, so it can use just one processor. This is the
> > major slowdown case in your comparison.
> >
> > Compare make -j2 on the host and on the guest: there will still be some
> > slowdown, but not such an high one. Possibly on the guest make -j1 could
> > be better (it would be interesting).
>
> host # time make -j2
> real    1m54.358s
> user    3m9.300s
> sys     0m18.910s

Er, it seems that _I_ gave you a wrong suggestion - it is still using both 
processor (though not optimally), so "time make -j1" on _both_ the host and 
the guest is a fairer comparison.

The confusion was born since on a uniprocessor machine it is usually suggested 
to use make -j2. However, make -j2 on a dual core will use both processors.

> guest # time make -j2
> real    7m37.511s
> user    2m32.770s
> sys     0m23.200s
>
> guest # time make -j1
> real    7m41.003s
> user    2m33.880s
> sys     0m23.230s
>
> :-( '''
> :
> > Also, the user time is less on UML. The fact that total time is higher is
> > probably due to running with -j3 on a uniprocessor machine, and the fact
> > that the user time is less is probably due to using gcc 3.3 rather than 4
> > (I seem to recall gcc 4 is slower in compilation than gcc 3).

-- 
Inform me of my mistakes, so I can add them to my list!
Paolo Giarrusso, aka Blaisorblade
http://www.user-mode-linux.org/~blaisorblade
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