[PATCH] dma-buf: Enhance dma-fence tracing

[Michael Sartain]

On Mon, Jan 21, 2019, at 4:20 PM, Chris Wilson wrote:
> Rather than every backend and GPU driver reinventing the same wheel for
> user level debugging of HW execution, the common dma-fence framework
> should include the tracing infrastructure required for most client API
> level flow visualisation.
> 
> With these common dma-fence level tracepoints, the userspace tools can
> establish a detailed view of the client <-> HW flow across different
> kernels. There is a strong ask to have this available, so that the
> userspace developer can effectively assess if they're doing a good job
> about feeding the beast of a GPU hardware.
...

I've got a first pass of this visualizing with gpuvis. Screenshots:

; with dma_event tracepoints patch
https://imgur.com/a/MwvoAYY

; with old i915 tracepoints
https://imgur.com/a/tG2iyHS

Couple questions...

With your new dma_event traceponts patch, we're still getting these
tracepoints:

  i915_request_in
  i915_request_out
  intel_engine_notify

And the in/out tracepoints line up with dma_fence_executes
(same ctx:seqno and time):

 <idle>-0     [006]   150.376273: dma_fence_execute_start: context=31, seqno=35670, hwid=0
 <idle>-0     [006]   150.413215: dma_fence_execute_end: context=31, seqno=35670, hwid=0

 <idle>-0     [006]   150.376272: i915_request_in:      dev=0, engine=0:0, hw_id=4, ctx=31, seqno=35670, prio=0, global=41230, port=1
 <idle>-0     [006]   150.413217: i915_request_out:     dev=0, engine=0:0, hw_id=4, ctx=31, seqno=35670, global=41230, completed?=1

However I'm also seeing several i915_request_in --> intel_engine_notify
tracepoints that don't have dma_fence_execute_* tracepoints:

    RenderThread-1279  [001]   150.341336: dma_fence_init:       driver=i915 timeline=ShooterGame[1226]/2 context=31 seqno=35669
    RenderThread-1279  [001]   150.341352: dma_fence_emit:       context=31, seqno=35669
          <idle>-0     [006]   150.376271: i915_request_in:      dev=0, engine=0:0, hw_id=4, ctx=31, seqno=35669, prio=0, global=41229, port=1
          <idle>-0     [006]   150.411525: intel_engine_notify:  dev=0, engine=0:0, seqno=41229, waiters=1
    RenderThread-1279  [001]   150.419779: dma_fence_signaled:   context=31, seqno=35669
    RenderThread-1279  [001]   150.419838: dma_fence_destroy:    context=31, seqno=35669

I assume something is going on at a lower level that we can't get the
information for via dma_fence?

Thanks!