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

Avi Kivity
2009-03-29T12:03:46Z

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.

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