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

[Jan Kiszka]

On 2012-09-14 12:20, Daniel P. Berrange wrote:
> 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

There is a nice comment by Steven that I pinned on my wall, the last
paragraph text-marked:
http://lkml.indiana.edu/hypermail/linux/kernel/1206.1/00445.html. These
days, I prefer to just point people to that printout instead of arguing.
Didn't help yet, unfortunately, to convince our corporate VPN vendor to
finally support 64-bit with his proprietary clients. Maybe because they
didn't visit my office yet.

The problem is also that some distros default the download to 32-bit
when asking for a desktop, e.g. Ubuntu or OpenSUSE. Kudos to Fedora for
not doing this.

Jan

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