[Intel-gfx] [PATCH RFC] Batchbuffer queue latency tracking v.1

[Ben Gamari]

Hey all,

Here is another patch requested by ickle. This time, we are attempting to track
the aggregate queue latency of requests. We record the time at which the
batch is emitted and then record its predecessor's completion time in a ringbuffer.
This is later processed by a delayed work function which looks up the request from its
sequence number and computes the latency, adding it to the device's accumulator. This
information is exposed through the seqno debugfs file. Let me know what you think,

- Ben