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

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Date:	Wed, 04 Apr 2007 08:43:39 -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:
> the main metric we are interested in is the overhead for people who just 
> want to run the non-patched native kernel that has CONFIG_PARAVIRT 
> enabled (99%+ of the users at the moment), so the delta is:
>
>  null:              +12.0%
>  null IO:            +7.5%
>  stat:        within noise
>  open/close:  within noise
>  TCP:                ~5.0%
>  signal install:      2.0%
>  signal handle:       4.7%
>  fork:                2.7%
>  exec:                3.6%
>  shell:               3.6%
>   
Hm, I don't think you can get this much precision out of these numbers. 
I noticed larger variations from boot-to-boot running the same test.

> 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.

>> paravirt, patching
>> ezr       Linux 2.6.21- 1000 0.25 0.53 31.8 34.4 10.1 1.04 5.44 730. 1583 4600
>> ezr       Linux 2.6.21- 1000 0.26 0.55 32.1 35.2 13.3 1.03 5.48 748. 1589 4606
>> ezr       Linux 2.6.21- 1000 0.26 0.54 32.0 34.9 14.1 1.04 5.43 752. 1606 4647
>>     
>
> i guess this pretty much makes the case for patching ...
>   

Right, that's why there's patching.


    J
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