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

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.

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'?)


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