From: Avi Kivity <avi@redhat.com>
To: Gerd Hoffmann <kraxel@redhat.com>
Cc: Stefan <kvm@pms.ifi.lmu.de>, kvm@vger.kernel.org
Subject: Re: 64 bit guest much faster ?
Date: Mon, 26 Oct 2009 12:12:13 +0200 [thread overview]
Message-ID: <4AE575FD.6010801@redhat.com> (raw)
In-Reply-To: <4AE564C6.3040605@redhat.com>
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.
--
error compiling committee.c: too many arguments to function
next prev parent reply other threads:[~2009-10-26 10:12 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-10-23 15:54 64 bit guest much faster ? Stefan
2009-10-25 5:41 ` Avi Kivity
2009-10-26 8:58 ` Gerd Hoffmann
2009-10-26 10:12 ` Avi Kivity [this message]
2009-10-26 10:42 ` Michael Tokarev
2009-10-26 10:44 ` Avi Kivity
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