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

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Message-Id: <1172100002.13378.42.camel@localhost.localdomain>
Date:	Thu, 22 Feb 2007 10:20:02 +1100
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Andi Kleen <ak@...e.de>
Cc:	virtualization@...ts.osdl.org, Chris Wright <chrisw@...s-sol.org>,
	xen-devel@...ts.xensource.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 05/24] Xen-paravirt_ops: Add pagetable accessors to
	pack and unpack pagetable entries

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?
Rusty.
PS. I really must revise my "paravirt-ops counter" patch which tallies
how much each op is getting called.


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