[Engine-devel] what does engine with cpuIdle?

[Dan Kenigsberg]

On Tue, Sep 11, 2012 at 08:52:51AM -0400, Laszlo Hornyak wrote:
> 
> 
> ----- Original Message -----
> > From: "Dan Kenigsberg" <danken at redhat.com>
> > To: "Laszlo Hornyak" <lhornyak at redhat.com>
> > Cc: "engine-devel" <engine-devel at ovirt.org>, "Omer Frenkel" <ofrenkel at redhat.com>
> > Sent: Tuesday, September 11, 2012 2:34:13 PM
> > Subject: Re: [Engine-devel] what does engine with cpuIdle?
> > 
> > On Tue, Sep 11, 2012 at 07:38:11AM -0400, Laszlo Hornyak wrote:
> > > 
> > > ----- Original Message -----
> > > > From: "Dan Kenigsberg" <danken at redhat.com>
> > > > To: "Omer Frenkel" <ofrenkel at redhat.com>
> > > > Cc: "Laszlo Hornyak" <lhornyak at redhat.com>, "engine-devel"
> > > > <engine-devel at ovirt.org>
> > > > Sent: Tuesday, September 11, 2012 9:22:15 AM
> > > > Subject: Re: [Engine-devel] what does engine with cpuIdle?
> > > > 
> > > > On Tue, Sep 11, 2012 at 01:55:01AM -0400, Omer Frenkel wrote:
> > > > > 
> > > > > 
> > > > > ----- Original Message -----
> > > > > > From: "Laszlo Hornyak" <lhornyak at redhat.com>
> > > > > > To: "engine-devel" <engine-devel at ovirt.org>
> > > > > > Sent: Monday, September 10, 2012 3:51:59 PM
> > > > > > Subject: [Engine-devel] what does engine with cpuIdle?
> > > > > > 
> > > > > > hi,
> > > > > > 
> > > > > > I am trying to change a behavior in vdsm. When you pass 100%
> > > > > > load
> > > > > > on
> > > > > > a VM, it will stop reporting further load and will keep
> > > > > > telling
> > > > > > 100%
> > > > > > until the load drops under 100% again in it's cpuIdle
> > > > > > information.
> > > > > > This is totally correct if you have only single-cpu VM's, but
> > > > > > it
> > > > > > is
> > > > > > false when you have multiple vcpu's, I think the cpuIdle
> > > > > > information
> > > > > > should not be on a 0-100 scale, but on a 0-100*vcpus scale.
> > > > > > 
> > > > > > So I submitted this patch to vdsm:
> > > > > > http://gerrit.ovirt.org/#/c/7892/2
> > > > > > and Dan pointed out that some functionality may depend on the
> > > > > > value
> > > > > > in the 0-100 interval. For me it seems it is ignored and the
> > > > > > load
> > > > > > is
> > > > > > calculated only from sysCpu + userCpu. Does anyone build on
> > > > > > the
> > > > > > cpuIdle value?
> > > > > > 
> > > > > > Thanks,
> > > > > > Laszlo
> > > > > >
> > > > > 
> > > > > you are right, engine doesn't save cpuIdle for vm,
> > > > > so it's not in use in the engine.
> > > > 
> > > > Laszlo, in this case, I think it would be best to drop this bogus
> > > > piece
> > > > of information.
> > > 
> > > Ok.
> > > 
> > > However, before I abandon this patch:
> > 
> > Why abandon? I've suggested you to keep it, just make it even
> > simpler.
> 
> Ok, it is only burocracy, but the new patch will do something
> completely different than the original, so it does not seem to make
> sense to continue this patch. It is more simple to make another one.

Actually, if the patch has the same intentions, I prefer to keep it as
another version - this way it is easier to see if former comments have
been addressed. But it's your code and your call.

> 
> > 
> > > we have a requirement to report cpuSys and cpuUser separately.
> > > Afaik
> > > in libvirt cpuUser and cpuSys does not include the actual guest
> > > time
> > > (at least not with KVM), and in this way if we only report cpuSys
> > > and
> > > cpuUser, the sum does not give the actual load, only a relatively
> > > little percentage of it.
> > 
> > I am not sure I understand what you are saying, but afaik, libvirt's
> > relatively-new
> > http://libvirt.org/html/libvirt-libvirt.html#virDomainGetCPUStats
> > reports the cpu time spent by the entire qemu process - in guest and
> > host modes.
> 
> It seems like sysCpu + userCpu < cpuTime, therefore something is
> missing. I will give it another try, maybe something wrong with my
> hosts.

I may well be wrong.
http://libvirt.org/html/libvirt-libvirt.html#VIR_DOMAIN_CPU_STATS_CPUTIME

someone would have to compare your report requirement with what libvirt
provides.

> 
> > 
> > > If we have the cpuIdle information in engine,
> > > we can calculate the guest time. Therefore, should I - include the
> > > guest time in cpuSys or cpuUser?
> > > - add another exported field?
> > > 
> > > And in both case, we will still have to calculate from cpuIdle
> > > because
> > > libvirt does not tell the guest cpu time :-(
> > 
> > Now I'm completely at loss. Why should we calculate cpuIdle per VM?
> > Haven't we agreed that it is useless?
> 
> Well, if libvirt exports the guest time in sysCpu, then we do not have
> to. But it seems it does not.

Even we should jump throguh hoops to get the data you require, I do not
see how cpuIdle is related (or actually, what it means).

Dan.