Re: [PATCH 0/7] Support for GB pages in KVM

Joerg Roedel
2009-03-29T12:47:59Z

On Sun, Mar 29, 2009 at 03:03:28PM +0300, Avi Kivity wrote:
> Joerg Roedel wrote:
>> On Sat, Mar 28, 2009 at 06:40:08PM -0300, Marcelo Tosatti wrote:
>>
>>> On Fri, Mar 27, 2009 at 03:31:52PM +0100, Joerg Roedel wrote:
>>>
>>>> Hi,
>>>>
>>>> this patchset extends the KVM MMU implementation to support 1GB pages as
>>>> supported by AMD family 16 processors. These patches enable support for
>>>> 1 GB pages with Nested Paging. Support for these pages in the shadow
>>>> paging code was also developed but does not run stable yet. The patch
>>>> for shadow-paging support is not included in this series and will be
>>>> sent out seperatly.
>>>>
>>> Looks generally sane. I'm not sure its even worthwhile to support
>>> GBpages with softmmu, because the chance of finding an area without
>>> shadowed (write protected) pages is much smaller than with 2MB pages.
>>>
>>
>> Thanks for your review.
>>
>> The idea behind GB pages in softmmu code was to provide GB pages to the
>> guest even if hardware does not support it. This would work better with
>> live migration (Only case where we wouldn't have gbpages then would be
>> vmx with ept enabled).
>>
>>
>>> Have any numbers to share?
>>>
>>
>> No numbers I fully trust by now. I measured a 32% improvement in
>> kernbench using nested pages backed with gb pages. I will do some more
>> measurements and share some more solid numbers.
>>
>>
>
> Compared to 2M pages? But we're already close to native here.

Yes, thats why I don't trust those numbers. I'll find out what went
wrong and provide more solid numbers.

Joerg