[Intel-gfx] [RFC 00/14] i915 PMU and engine busy stats

[Chris Wilson]

Quoting Tvrtko Ursulin (2017-07-18 15:36:04)
> From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> 
> Rough sketch of the idea I mentioned a few times to various people - merging
> the engine busyness tracking with Chris i915 PMU RFC.
> 
> First patch is the actual PMU RFC by Chris. It is followed by some cleanup
> patches, then come a few improvements, cheap execlists engine busyness tracking,
> debugfs view for the same, and finally the i915 PMU is extended to use this
> instead of timer based mmio sampling.
> 
> This makes it cheaper and also more accurate since engine busyness is not
> derived via sampling.
> 
> But I haven't figure out the perf API yet. For example is it possible to access
> our events in an usable fashion via perf top/stat or something? Do we want to
> make the events discoverable as I did (patch 8).

In my dreams I have gpu activity in the same perf timechart as gpu
activity. But that can be mostly by the request tracepoints, but still
overlaying cpu/gpu activity is desirable and more importantly we want to
coordinate with nouveau/amdgpu so that such interfaces are as agnostic
as possible. There are definitely a bunch of global features in common
for all (engine enumeration & activity, mempool enumeration, size &
activty, power usage?). But the key question is how do we build for the
future? Split the event id range into common/driver?

> I could not find much (any?) kernel API level documentation for perf.

There isn't much indeed. Given that we now have a second pair of eyes go
over the sampling and improve its interaction with i915, we should start
getting PeterZ involved to check the interaction with perf.
 
> Btw patch series actually works since intel-gpu-overlay can use these events
> when they are available.
> 
> Chris Wilson (1):
>   RFC drm/i915: Expose a PMU interface for perf queries

One thing I would like is for any future interface (including this
engine/class/event id) to use the engine class/instance mapping.
-Chris