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

Anthony Liguori
2010-03-16T17:06:19Z

On 03/16/2010 08:08 AM, Ingo Molnar wrote:
> * Avi Kivity<avi@redhat.com> wrote:
>
>
>> On 03/16/2010 02:29 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.
>
> 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.
>

You're making too many assumptions.

There is no list of guests anymore than there is a list of web browsers.

You can have a multi-tenant scenario where you have distinct groups of
virtual machines running as unprivileged users.

> 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.
>

Does "perf kvm list" always run as root? What if two unprivileged users
both have a VM named "Fedora"?

If we look at the use-case, it's going to be something like, a user is
creating virtual machines and wants to get performance information about
them.

Having to run a separate tool like perf is not going to be what they
would expect they had to do. Instead, they would either use their
existing GUI tool (like virt-manager) or they would use their management
interface (either QMP or libvirt).

The complexity of interaction is due to the fact that perf shouldn't be
a stand alone tool. It should be a library or something with a
programmatic interface that another tool can make use of.

Regards,

Anthony Liguori

> 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?
>
> Ingo
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