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

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Date:	Wed, 4 Apr 2007 13:47:42 +0200
From:	Andi Kleen <ak@...e.de>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	virtualization@...ts.osdl.org, lkml <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [patch 04/17] Add pagetable accessors to pack and unpack pagetable entries

On Wednesday 04 April 2007 11:25:57 Jeremy Fitzhardinge wrote:
> Andi Kleen wrote:
> > What do the benchmarks say with CONFIG_PARAVIRT on native hardware
> > compared to !CONFIG_PARAVIRT. e.g. does lmbench suffer? 
> 
> Barely.  There's a slight hit for not using patching, and patching is
> almost identical to native performance.  The most noticeable difference
> is in the null syscall microbenchmark, but once you get to complex
> things the difference is in the noise.

Why is there a difference for null syscall? I had assumed we patched all the 
fast path cases relevant there. Do you have an idea where it comes from?

-Andi
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