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

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Message-ID: <45DCD559.1040301@goop.org>
Date:	Wed, 21 Feb 2007 15:27:21 -0800
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Rusty Russell <rusty@...tcorp.com.au>
CC:	Andi Kleen <ak@...e.de>, Chris Wright <chrisw@...s-sol.org>,
	virtualization@...ts.osdl.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	xen-devel@...ts.xensource.com, linux-kernel@...r.kernel.org
Subject: Re: [Xen-devel] Re: [patch 05/24] Xen-paravirt_ops: Add pagetable
 accessors to pack and unpack pagetable entries

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
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