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

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Date:	Wed, 04 Apr 2007 09:10:16 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Andi Kleen <ak@...e.de>, Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [patch 04/17] Add pagetable accessors to pack and unpack pagetable
 entries

Ingo Molnar wrote:
> sure. i simply took the middle numbers. But there's definitely a 'few 
> percents' trend in the numbers.
>   

Yep. I guess the thing that coloured my summary is that I found overhead
of unpatched paravirt_ops calls surprisingly small.  I was really
expecting more like ~10% hit, but only null syscall approached that.

>>> this is not 'barely measurable' but 'BLOODY LARGE' overhead.
>>>       
>> Yes.  Fortunately there's a noticable difference between native and 
>> unpatched paravirt, because it shows all the effort we put into 
>> patching is worthwhile.
>>     
>
> if only it were not such an ugly piece of code? ;)
>   

Sigh, yes.  I've cleaned it up a bit since the last post, and commented
it, but I couldn't do much with its essential ugliness.  But I guess it
just got promoted from "ugly" to "ugly but necessary".

    J
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