[Intel-gfx] [RFC 08/11] drm/i915: Export engine busy stats in debugfs

[Chris Wilson]

Quoting Tvrtko Ursulin (2017-09-11 16:25:56)
> From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> 
> Export the stats added in the previous patch in debugfs.
> 
> Number of active clients reading this data is tracked and the
> static key is only enabled whilst there are some.
> 
> Userspace is intended to keep the file descriptor open, seeking
> to the beginning of the file periodically, and re-reading the
> stats.
> 
> This is because the underlying implementation is costly on every
> first open/last close transition, and also, because the stats
> exported mostly make sense when they are considered relative to
> the previous sample.
> 
> File lists nanoseconds each engine was active since the tracking
> has started.

Purpose? It's a debug API, so what are we debugging and by whom?
-Chris