linux-kernel - Re: [kvm-devel] [PATCH 0/2][KVM] guest time accounting

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Message-ID: <46C0693A.1080900@bull.net>
Date:	Mon, 13 Aug 2007 16:22:50 +0200
From:	Laurent Vivier <Laurent.Vivier@...l.net>
To:	Christian Borntraeger <borntraeger@...ibm.com>
Cc:	kvm-devel@...ts.sourceforge.net,
	linux-kernel <linux-kernel@...r.kernel.org>, cotte@...ibm.com
Subject: Re: [kvm-devel] [PATCH 0/2][KVM] guest time accounting

Christian Borntraeger wrote:
> Am Freitag, 10. August 2007 schrieb Laurent Vivier:
>> The aim of these two patches is to measure the CPU time used by a virtual
>> machine. All comments are welcome... I'm not sure it's the good way to do 
> that.
> 
> I did something similar for or s390guest prototype, that Carsten posted in 
> May.  I decided to account guest time to the user process instead of adding a 
> new field to avoid hazzle with old top. As you can read in the patch comment, 
> I personally prefer a new field if we can get one.
> 
> My implementation uses a similar mechanism like hard and softirq. So I have an 
> sie_enter an sie_exit and a task_is_in_sie function - like irq_enter and 
> irq_exit. The main difference is based on the fact, that s390 has precise 
> accouting for irq, steal, user and system time, and therefore my patch is 
> based on architecture specifc code using CONFIG_VIRT_CPU_ACCOUNT. 
> 
> In general my patch has the same idea as your patch, so I am going to review 
> your patch and see if it would fit for s390.
> 
> For reference this is the (never posted) old patch for our virtualisation 
> prototype. It wont work with kvm but it gives you the idea what we had in 
> mind on s390.
> 

thank you for your comment.

As virtualization becomes very popular, perhaps we should implement something
which could be used by all linux supported architectures ?
(yes, I know it's non-sense for archs like m68k...)
But my [PATCH 1/2] can be a good start (adding "guest" in cpustat)
As guest accounting is hw dependent, I think we should add a hook in the
accounting functions.

Laurent
-- 
------------- Laurent.Vivier@...l.net  --------------
          "Software is hard" - Donald Knuth


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