[Intel-gfx] [RFC 0/3] Engine utilization tracking

[Chris Wilson]

On Tue, May 09, 2017 at 04:16:41PM +0100, Tvrtko Ursulin wrote:
> 
> On 09/05/2017 15:26, Chris Wilson wrote:
> >On Tue, May 09, 2017 at 03:09:33PM +0100, Tvrtko Ursulin wrote:
> >>From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> >>
> >>By popular customer demand here is the prototype for cheap engine utilization
> >>tracking.
> >
> >customer and debugfs?
> 
> Well I did write in one of the following paragraphs on this topic.
> Perhaps I should have put it in procfs. :) Sysfs API looks
> restrictive or perhaps I missed a way to get low level (fops) access
> to it.
> 
> >>It uses static branches so in the default off case it really should be cheap.
> >
> >Not as cheap (for the off case) as simply sampling RING_HEAD/RING_TAIL
> 
> Off case are three no-op instructions in three places in the irq
> tasklet. And a little bit of object size growth, if you worry about
> that aspect?

It's just how the snowball begins.
 
> >which looks to be the same level of detail. I wrapped all this up in a
> >perf interface once up a time...
> 
> How does that work? Via periodic sampling? Accuracy sounds like it
> would be proportionate to the sampling frequency, no?

Right, and the sampling frequency is under user control (via perf) with
a default of around 1000, gives a small systematic error when dealing with %

I included power, interrupts, rc6, frequency (and the statistics but I
never used those and dropped them once oa landed), as well as
utilisation, just for the convenience of having sane interface :)
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre