linux-kernel - Re: [PATCH 0/11] VMI / Paravirt bugfixes for 2.6.21

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Date:	Tue, 06 Feb 2007 01:25:07 -0800
From:	Zachary Amsden <zach@...are.com>
To:	Arjan van de Ven <arjan@...radead.org>
CC:	Rusty Russell <rusty@...tcorp.com.au>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...l.org>, Andi Kleen <ak@....de>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Chris Wright <chrisw@...s-sol.org>
Subject: Re: [PATCH 0/11] VMI / Paravirt bugfixes for 2.6.21

Arjan van de Ven wrote:
> On Tue, 2007-02-06 at 16:11 +1100, Rusty Russell wrote:
>   
>> On Mon, 2007-02-05 at 20:54 -0800, Zachary Amsden wrote:
>>     
>>> Rusty Russell wrote:
>>>       
>>>> Indeed, I'm expecting to push lguest this week, and this code will
>>>> effect me, so I'd like to see this in a -mm soon...
>>>>         
>>> Yes, I took a look at the lguest changes today and I think these won't 
>>> generate conflicts, just make stuff easier for you ;)  Course you've now 
>>> got a couple new paravirt-ops to support, but the native ones are fine 
>>> for temporary use.
>>>       
>> Implementing stolen time is something I'd like to do, since it'd be a
>> nice self-contained example the expectations.
>>     
>
>
> hmm stolen time could even be useful without virtualization; to a large
> degree, if cpufreq reduces the speed of your cpu you have "stolen
> cycles" that way... I wonder if this concept can be used for that as
> well...
>   

Yes, stolen time happens in most moderns systems as a result of power 
management (and you can probably count SMM cycles as stolen if only 
there was a way to count them).  It would be useful to report on a 
laptop, for instance, how many cycles have been stolen by running off 
battery or on a server because of heat issues.  Having an interface for 
Linux to report this seems useful.  It is a covert channel, however, in 
a virtualized environment, so there should be some provision in the 
hypervisor to turn it off.

Zach
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