[Intel-gfx] [PATCH 3/8] drm/i915: Framework for capturing command stream based OA reports

[sourab gupta]

On Thu, 2017-03-16 at 01:10 -0700, Chris Wilson wrote:
> On Thu, Mar 16, 2017 at 11:44:10AM +0530, sourab.gupta at intel.com wrote:
> > @@ -3593,6 +3670,7 @@ void i915_oa_init_reg_state(struct intel_engine_cs *engine,
> >  void i915_oa_update_reg_state(struct intel_engine_cs *engine,
> >  			      struct i915_gem_context *ctx,
> >  			      uint32_t *reg_state);
> > +void i915_perf_command_stream_hook(struct drm_i915_gem_request *req);
> >  
> >  /* i915_gem_evict.c */
> >  int __must_check i915_gem_evict_something(struct i915_address_space *vm,
> > diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> > index aa75ea2..7af32c97 100644
> > --- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> > +++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> > @@ -1441,12 +1441,16 @@ static void eb_export_fence(struct drm_i915_gem_object *obj,
> >  	if (exec_len == 0)
> >  		exec_len = params->batch->size - params->args_batch_start_offset;
> >  
> > +	i915_perf_command_stream_hook(params->request);
> 
> Could you have named it anything more cyptic and inconsistent?

Sorry. Would 'i915_perf_capture_metrics' work?
Can you please suggest an appropriate name otherwise.
> 
> Quite clearly this can fail, so justify the non handling of errors.
> 
> DRM_ERROR is not error handling, it is an indication that this patch
> isn't ready.

Well, the intent was to have minimal effect to execbuf normal routine,
even if we fail. But, I guess I'm mistaken.
I'll rectify this to handle the case, if perf callback fails.
	
> 
> > +void i915_perf_command_stream_hook(struct drm_i915_gem_request *request)
> > +{
> > +	struct intel_engine_cs *engine = request->engine;
> > +	struct drm_i915_private *dev_priv = engine->i915;
> > +	struct i915_perf_stream *stream;
> > +
> > +	if (!dev_priv->perf.initialized)
> > +		return;
> > +
> > +	mutex_lock(&dev_priv->perf.streams_lock);
> 
> Justify a new global lock very, very carefully on execbuf.

The lock introduced here is to protect the the perf.streams list against
addition/deletion while we're processing the list during execbuf call.
The other places where the mutex is taken is when a new stream is being
created (using perf_open ioctl) or a stream is being destroyed
(perf_release ioctl), which just protect the list_add and list_del into
the perf.streams list.
As such, there should not be much impact on execbuf path.
Does this seem reasonable?

> 
> > +	list_for_each_entry(stream, &dev_priv->perf.streams, link) {
> > +		if ((stream->state == I915_PERF_STREAM_ENABLED) &&
> > +					stream->cs_mode)
> > +			stream->ops->command_stream_hook(stream, request);
> > +	}
> > +	mutex_unlock(&dev_priv->perf.streams_lock);
> > +}
> 
> > +static void i915_perf_command_stream_hook_oa(struct i915_perf_stream *stream,
> > +					struct drm_i915_gem_request *request)
> > +{
> > +	struct drm_i915_private *dev_priv = request->i915;
> > +	struct i915_gem_context *ctx = request->ctx;
> > +	struct i915_perf_cs_sample *sample;
> > +	u32 addr = 0;
> > +	u32 cmd, *cs;
> > +
> > +	sample = kzalloc(sizeof(*sample), GFP_KERNEL);
> > +	if (sample == NULL) {
> > +		DRM_ERROR("Perf sample alloc failed\n");
> > +		return;
> > +	}
> > +
> > +	cs = intel_ring_begin(request, 4);
> > +	if (IS_ERR(cs)) {
> > +		kfree(sample);
> > +		return;
> > +	}
> > +
> > +	sample->ctx_id = ctx->hw_id;
> > +	i915_gem_request_assign(&sample->request, request);
> 
> > +
> > +	i915_gem_active_set(&stream->last_request, request);
> 
> Hint, you don't need you own request trap.
Sorry, I didn't understand you fully here. I'm storing the reference to
the last active request associated with the stream inside the
last_request 'gem_active' field. Do I need to do something differently
here?

> -Chris
>