RE: [Xen-users] understanding xm top

["Petersson, Mats" <Mats.Petersson@xxxxxxx>]

> -----Original Message-----
> From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx 
> [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of 
> Ulrich Windl
> Sent: 20 November 2006 09:14
> To: xen-users@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [Xen-users] understanding xm top
> 
> On 20 Nov 2006 at 13:10, Julian Davison wrote:
> 
> > Ulrich Windl wrote:
> > > On 15 Nov 2006 at 14:53, Tommie McAfee wrote:
> > > 
> > >>>  If xm top shows 10% CPU utilization for domain0, it 
> means the CPU
> > >>> utilization in domain0 is 10% of FOUR physcial CPUs. Is 
> this right?
> > >>>
> > >>
> > >> I  don't think the values scale that way percentage 
> wise, because with 4
> > >> physical cpu's, xm-top can show CPU(%) to be as high as 
> 400%.  Unlike the
> > > 
> > > IMHO that's about as stupid as this output from procinfo:
> > > 
> > > idle  :   3d 16:05:53.82  99.8%
> > > uptime:      22:03:12.95
> > > 
> > > How can the idle time be longer than the uptime? How can 
> the CPU usage be more 
> > > than 100%?
> > 
> > Because it's idle time for all the processors. In any given
> > day, with a dual-processor machine, you get two days worth
> > of CPU to use (1 day for each processor).
> > It's curious that people are more interested in how much
> > aggregated idle time their CPU(s) have, but only how long
> > the entire box has been powered up.
> 
> It's still stupid, because when four CPUs are up, the uptime 
> could also be 
> multiplied by four. I still believe, CPU usage, cumulated or 
> not cannot be higher 
> than 100%, just as the idle time proportion cannot exceed 100%.

No, and it says that it's 99.8%, so what's wrong? 

It's just that the total CPU-time spent in idle is four times 99.8% of
22:03:12.95, which I presume makes 3d 16:05:53.82 (I haven't calculated
it myself, but 22 * 4 = 88 hours, 3 * 24 = 72 + 16 -> 88 hours, so we're
not far off... 

Uptime is simply the time that the machine has been running from the
time it started until now - which should not be multiplied by 4, as the
machine is only one machine. The amount of time that is idle for the
system is the amount of CPU-seconds (or whatever unit you prefer to use)
that the CPU is not doing something useful. Since you have 4 CPU's, it
will be four seconds of idle for evey second the entire system is idle. 

It's still not higher than 100% of the available CPU-time, as that's
always going to be one second per CPU per second, if you see what I
mean... 

Did this explain better, or are you still confused?

--
Mats

> 
> Ulrich
> 
> 
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