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

[Jan Kiszka]

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.

> 
> Thank you for the clarification -- very useful information indeed!
> 
> /mjt
> 

You are welcome.

Jan

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