linux-kernel - Re: [kvm-devel] Réf. : Re: [PATCH 0/4] Virtual Machine Time Accounting

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Message-Id: <200708211006.42938.borntraeger@de.ibm.com>
Date:	Tue, 21 Aug 2007 10:06:42 +0200
From:	Christian Borntraeger <borntraeger@...ibm.com>
To:	kvm-devel@...ts.sourceforge.net
Cc:	"Glauber de Oliveira Costa" <glommer@...il.com>,
	"laurent.vivier@...l.net" <laurent.vivier@...l.net>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	John Stoffel <john@...ffel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	virtualization <virtualization@...ts.linux-foundation.org>
Subject: Re: [kvm-devel] Réf. : Re: [PATCH 0/4] Virtual Machine Time Accounting

Am Montag, 20. August 2007 schrieb Glauber de Oliveira Costa:
> Although I don't know KVM to a that deep level, I think it should be
> possible to keep the virtual cpus in different process (or threads),
> and take the accounting time from there. Perfectly possible to know
> the time we spent running (user time), and the time the hypervisor
> spent doing things on our behalf (system time).

I disagree here. First thing, you dont want to have the virtual cpu in a 
different process than the hypervisor control code for that cpu. Otherwise  
communication has to be made via IPC. 
Secondly, Its not qemu/kvm that does the accouting. Its existing userspace 
code like top/snmp agents and clients! etc. that would require additional 
knowledge which thread is guest code.

I personally like the approach Laurent has taken. Maybe it needs some polish 
and maybe we want an account_guest_time function, but in general I think he 
is doing the right thing. 

Christian
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