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

[Tvrtko Ursulin]

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?

> 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?

Regards,

Tvrtko