Re: [Xen-devel] Re: [patch 05/24] Xen-paravirt_ops: Add pagetable accessors to pack and unpack pagetable entries

Jeremy Fitzhardinge
2007-02-21T23:27:32Z

Rusty Russell wrote:
> On Wed, 2007-02-21 at 23:15 +0100, Andi Kleen wrote:
>
>> On Wednesday 21 February 2007 21:52, Jeremy Fitzhardinge wrote:
>>
>>> Add a set of accessors to pack, unpack and modify page table entries
>>> (at all levels). This allows a paravirt implementation to control the
>>> contents of pgd/pmd/pte entries. For example, Xen uses this to
>>> convert the (pseudo-)physical address into a machine address when
>>> populating a pagetable entry, and converting back to pphys address
>>> when an entry is read.
>>>
>> Do you have some lmbench numbers before/after this change?
>> iirc at least fork and exit do a lot of pte accesses in various forms.
>> If it's measurable it might be needed to patch those for the native case.
>>
>
> Yes, __mkpte must be patched to avoid performance embarrassment.
>
> Jeremy, did you want me to do this, or are you happy to?
>
I'm working on it now. I'll mail out a proposal in a little bit.

J