linux-kernel - Re: [PATCH] Enhance perf to collect KVM guest os statistics from host side

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Date:	Tue, 16 Mar 2010 15:16:48 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Sheng Yang <sheng@...ux.intel.com>,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	Marcelo Tosatti <mtosatti@...hat.com>,
	oerg Roedel <joro@...tes.org>,
	Jes Sorensen <Jes.Sorensen@...hat.com>,
	Gleb Natapov <gleb@...hat.com>,
	Zachary Amsden <zamsden@...hat.com>, ziteng.huang@...el.com
Subject: Re: [PATCH] Enhance perf to collect KVM guest os statistics from
 host side

On 03/16/2010 03:08 PM, Ingo Molnar wrote:
>
>>> I mean, i can trust a kernel service and i can trust /proc/kallsyms.
>>>
>>> Can perf trust a random process claiming to be Qemu? What's the trust
>>> mechanism here?
>>>        
>> Obviously you can't trust anything you get from a guest, no matter how you
>> get it.
>>      
> I'm not talking about the symbol strings and addresses, and the object
> contents for allocation (or debuginfo). I'm talking about the basic protocol
> of establishing which guest is which.
>    

There is none.  So far, qemu only dealt with managing just its own 
guest, and left all multiple guest management to higher levels up the 
stack (like libvirt).

> I.e. we really want to be able users to:
>
>   1) have it all working with a single guest, without having to specify 'which'
>      guest (qemu PID) to work with. That is the dominant usecase both for
>      developers and for a fair portion of testers.
>    

That's reasonable if we can get it working simply.

>   2) Have some reasonable symbolic identification for guests. For example a
>      usable approach would be to have 'perf kvm list', which would list all
>      currently active guests:
>
>       $ perf kvm list
>         [1] Fedora
>         [2] OpenSuse
>         [3] Windows-XP
>         [4] Windows-7
>
>      And from that point on 'perf kvm -g OpenSuse record' would do the obvious
>      thing. Users will be able to just use the 'OpenSuse' symbolic name for
>      that guest, even if the guest got restarted and switched its main PID.
>
> Any such facility needs trusted enumeration and a protocol where i can trust
> that the information i got is authorative. (I.e. 'OpenSuse' truly matches to
> the OpenSuse session - not to some local user starting up a Qemu instance that
> claims to be 'OpenSuse'.)
>
> Is such a scheme possible/available? I suspect all the KVM configuration tools
> (i havent used them in some time - gui and command-line tools alike) use
> similar methods to ease guest management?
>    

You can do that through libvirt, but that only works for guests started 
through libvirt.  libvirt provides command-line tools to list and manage 
guests (for example autostarting them on startup), and tools built on 
top of libvirt can manage guests graphically.

Looks like we have a layer inversion here.  Maybe we need a plugin 
system - libvirt drops a .so into perf that teaches it how to list 
guests and get their symbols.

-- 
error compiling committee.c: too many arguments to function

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