Re: [Qemu-devel] qemu-system-i386 vs qemu-system-x86_64 ?

[Daniel P. Berrange]

On Fri, Sep 14, 2012 at 12:12:43PM +0200, Jan Kiszka wrote:
> On 2012-09-14 12:03, Michael Tokarev wrote:
> > On 14.09.2012 14:00, Jan Kiszka wrote:
> > []
> >> The major difference in qemu-system-i386 vs. qemu-system-x86_64 is on
> >> the TCG side: We measured noticeable performance benefits when running
> >> 32/16 bit OSes against qemu-system-i386 vs. using qemu-system-x86_64. I
> >> don't have numbers at hand, but colleagues decided to use the 32-bit
> >> version for that reason (when no KVM is available).
> > 
> > Interesting.  Maybe someone should look at the difference on TCG side
> > and merge interesting bits from i386 to x86_64... :)
> 
> I suppose the difference - for our use cases at least - lies in the
> different register and address sizes. Maybe there is room for more
> runtime optimizations, we never looked in that details as -i386 still
> works fine. And, if you are on 32-bit host (see below) - but we aren't,
> qemu-system-x86_64 hurts even more.
> 
> > 
> > The thing is: x86_64 becomes the only x86 platform these days, or at
> > least the MAIN platform.
> 
> I know, and I'm telling everyone. Still, too many crazy people keep on
> installing 32-bit distros or even 32-bit kernels. Maybe x64-32 will
> improve this.

It is quite depressing that 32-bit still accounts for 55% of deployed
Fedora installs:

  http://smolt.fedoraproject.org/static/stats/stats.html

That said, a year ago it was even worse with 32-bit up in 70% region


Daniel
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