On Wed, Dec 13, 2017 at 06:53:14PM +0100, Thomas Trepl wrote:
> >
> > How do the 4 CPUs compare to what your host system offers ? My
> > impression has always been that *qemu* will not map CPUs 1:1 (there
> > is an overhead of running a VM) and for a big package that DOES make
> > a difference. But I have no idea about vmware.
> The physical box is a 16GB E3-1245 Xeon, showing 8 CPUs to the system.
> Sure, there is a bit of difference from VM compared to physical, but
> the system at all is that fast that I do not worry about.
>
[...]
>
> > If you only have 4 (real) cores, using -j6 on large C++ files is
> > unlikely to help - it might hinder, it might not make a lot of
> > difference.
> Well, i configured my VM to have 4 CPUs as many of the BLFS packages
> has a SBU number with a note like "XX SBU (using 4 cores)". So i made 4
> CPUs visible.
>
That sounds a reasonable approach, but I'm always dubious whether
times for a moderately-large package in a VM are similar to times on
real hardware. At the moment, taskset is my preference if I need to
measure on my 8-core machine (editor's guide, chapter 6).
FWIW I'm currently fighting firefox-58beta, and in this context both
current rustc (58 needs newer rust than what is in the book) and
firefox58 itself are using sufficiently recent versions of the
num_cpus cargo, so I'm hopeful I can again use taskset when the time
comes).
ĸen
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