[Vm-dev] 64 bit VM, source anyone?

goran at krampe.se goran at krampe.se
Wed Dec 5 08:17:03 UTC 2007


"Michael van der Gulik" <mikevdg at gmail.com> wrote:
> On Dec 5, 2007 10:23 AM, <goran at krampe.se> wrote:
> > PS. The reason I said "slowish" is that... well, it is definitely not
> > much faster than my Pentium-M laptop. But after talking on IRC it became
> > clear that those numbers may very well be the expected.
> Why would a 64-bit VM be slower?
> Would it be because it's moving twice as much memory around, or because it's
> fiddling with 32-bit pointers using 64-bit registers?
> Gulik.

Ok, some clarifications:

1. My numbers were for the 32-bit binary VM, not a 64 bit VM. 

2. There are reasons going both ways regarding speed. On the AMD64
architecture (see some details here: http://www.debian.org/ports/amd64)
there is potential for higher speed through better abilities for the
compiler BUT... there are also things slowing it down (8 bytes instead
of 4 in lots of situations). Also, I don't know how/if the gnuifier is
affected by this (perhaps not).

As Phillipe's post suggests - the 32 bit VM is actually a tad faster on
his box. It might be interesting to know if he has toyed with
optimization flags.

regards, Göran

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