Re: [RFC 08/11] drm/i915: Export engine busy stats in debugfs

Tvrtko Ursulin
2017-09-15T09:47:01Z

On 14/09/2017 21:17, Chris Wilson wrote:
> Quoting Tvrtko Ursulin (2017-09-11 16:25:56)
>> From: Tvrtko Ursulin <tvrtko.ursulin@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?

Now that perf stat works it has very little value indeed. Probably
serves as a reason to have the intel_enable_engines_stats API in. I
could drop it and move that API to the same patch which exports it?

Regards,

Tvrtko