linux-kernel - Re: [PATCH] xen: core dom0 support

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Message-ID: <49AEBCA2.8020307@goop.org>
Date:	Wed, 04 Mar 2009 09:38:42 -0800
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Anthony Liguori <anthony@...emonkey.ws>
CC:	Nick Piggin <nickpiggin@...oo.com.au>,
	Xen-devel <xen-devel@...ts.xensource.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	the arch/x86 maintainers <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] xen: core dom0 support

Anthony Liguori wrote:
> Jeremy Fitzhardinge wrote:
>> Nick Piggin wrote:
>
>> It really depends on the workload.  There's three cases to consider: 
>> software shadow pagetables, hardware nested pagetables, and Xen 
>> direct pagetables.  Even now, Xen's (highly optimised) shadow 
>> pagetable code generally out-performs modern nested pagetables, at 
>> least when running Windows (for which that code was most heavily tuned).
>
> Can you point to benchmarks?  I have a hard time believing this.

Erm, not that I know of off-hand.  I don't really have any interest in 
Windows performance, so I'm reduced to repeating (highly reliable) Xen 
Summit corridor chat.

> How can shadow paging beat nested paging assuming the presence of 
> large pages? 

I think large pages do turn the tables, and its close to parity with 
shadow with 4k pages on recent cpus.  But see above for reliability on 
that info.

    J

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