Re: [Xen-devel] trace IDLE VCPU using xenalyze --scatterplot-pcpu?

[George Dunlap <george.dunlap@xxxxxxxxxxxxx>]

On 27/03/13 02:15, Dario Faggioli wrote:
> On mar, 2013-03-26 at 14:12 -0500, Sisu Xi wrote:
> > Hi, All:
> Hi Sisu!
>
> > I was following the article here to plot the scheduler execution trace.
> > http://blog.xen.org/index.php/2012/09/27/tracing-with-xentrace-and-xenalyze/
> >
> > I was able to get the trace and plot it,
> EhEh, glad it was helpful! :-P
>
> > however, the trace for IDLE
> > VCPU is skipped. This makes it harder to understand the scheduler
> > behavior (For example, cap in credit).
> Mmmm... I think I see what you mean.
>
> > Does anyone know how to get the data for the IDLE VCPU when using
> > xenalyze --scatterplot-pcpu?
> Well, I double-checked and it is true that, at least here,
> --scatterplot-pcpu does not show the vCPUs of the idle domain. One could
> probably try to understand when they're scheduled by looking at when
> _no_other_ vCPU of any other domain runs on a particular pCPU (and
> considering that the idle domain has one vCPU pinned to each pCPU), but
> that would be quite unpractical I guess...
>
> Perhaps you can achieve something similar to what you need by looking
> for/plotting the runstate changes for the vCPUs of the idle domain
> (i.e., 32767vXX from `xenalyze --scatterplot-runstate') ?
>
> George, any other ideas?
Well, I always intendended xenalyze to be a tool you could modify to add 
functionality as-needed; more like a library of useful analytical 
functions than a finished product.  --scatterplot-pcpu doesn't show 
vcpus of the idle domain because I found it extraneous and confusing, so 
I excluded it:
    if ( opt.scatterplot_pcpu
         && next->d->did != IDLE_DOMAIN
         && next->d->did != DEFAULT_DOMAIN )
    {

If you just want to make the change locally, you can just take out the 
one line about the IDLE_DOMAIN.  I'd be happy to take a patch to 
xenalyze to add an option to show the idle domain as well.  (Maybe 
"--with-idle-domain" as a general way to say, 'don't exclude the idle 
domain from the output'?)
 -George

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