linux-kernel - Re: [patch 04/17] Add pagetable accessors to pack and unpack pagetable entries

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Date:	Mon, 02 Apr 2007 16:35:24 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Andi Kleen <ak@...e.de>
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>,
	virtualization@...ts.osdl.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [patch 04/17] Add pagetable accessors to pack and unpack
	pagetable entries

On Mon, 2007-04-02 at 08:12 +0200, Andi Kleen wrote:
> On Monday 02 April 2007 07:56, 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.
> 
> What do the benchmarks say with CONFIG_PARAVIRT on native hardware
> compared to !CONFIG_PARAVIRT. e.g. does lmbench suffer? 

This patch by itself, definitely: I gathered stats previously simply
measuring the number of calls, and it's comparable to the other calls we
had to patch.

So it's clear that the patch infrastructure needs to cover them.  We can
debate whether we should extend patching to everything as 1/17 does, or
just to mkpte and pteval.

I'd still like to see new microbench stats tho.

Cheers!
Rusty.

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