Re: 64 bit guest much faster ?

Avi Kivity
2009-10-26T10:12:12Z

On 10/26/2009 10:58 AM, Gerd Hoffmann wrote:
> On 10/23/09 17:54, Stefan wrote:
>>
>> Hello,
>>
>> I have a simple question (sorry I'm a kvm beginner):
>> Is it right that a 64bit guest (8 CPUs, 16GB) is
>> much faster than a 32bit guest (8 CPUs, 16GB PAE).
> ^^^^
> Yes. With *that* much memory the 32bit guest struggles with address
> space limitations (32bit -> 4G), whereas the 64bit guest doesn't.
>
> With up to 1G you shouldn't see a noticable difference. But the more
> highmem the 32bit guest uses the higher is the penalty. Especially
> without ept/npt as every kmap() of a high page is a roundtrip to the
> hypervisor then.
>

Oh yes, without ept/npt the slowdown should indeed be significant with
this much memory.

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