Re: [Intel-gfx] [PATCH 24/47] drm/i915/guc: Add several request trace points

[Matthew Brost <matthew.brost@intel.com>]

On Tue, Jul 13, 2021 at 10:06:17AM +0100, Tvrtko Ursulin wrote:
> 
> On 24/06/2021 08:04, Matthew Brost wrote:
> > Add trace points for request dependencies and GuC submit. Extended
> > existing request trace points to include submit fence value,, guc_id,
> > and ring tail value.
> > 
> > Cc: John Harrison <john.c.harrison@intel.com>
> > Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> > ---
> >   .../gpu/drm/i915/gt/uc/intel_guc_submission.c |  3 ++
> >   drivers/gpu/drm/i915/i915_request.c           |  3 ++
> >   drivers/gpu/drm/i915/i915_trace.h             | 39 ++++++++++++++++++-
> >   3 files changed, 43 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> > index 89b3c7e5d15b..c2327eebc09c 100644
> > --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> > +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> > @@ -422,6 +422,7 @@ static int guc_dequeue_one_context(struct intel_guc *guc)
> >   			guc->stalled_request = last;
> >   			return false;
> >   		}
> > +		trace_i915_request_guc_submit(last);
> >   	}
> >   	guc->stalled_request = NULL;
> > @@ -642,6 +643,8 @@ static int guc_bypass_tasklet_submit(struct intel_guc *guc,
> >   	ret = guc_add_request(guc, rq);
> >   	if (ret == -EBUSY)
> >   		guc->stalled_request = rq;
> > +	else
> > +		trace_i915_request_guc_submit(rq);
> >   	return ret;
> >   }
> > diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
> > index d92c9f25c9f4..7f7aa096e873 100644
> > --- a/drivers/gpu/drm/i915/i915_request.c
> > +++ b/drivers/gpu/drm/i915/i915_request.c
> > @@ -1344,6 +1344,9 @@ __i915_request_await_execution(struct i915_request *to,
> >   			return err;
> >   	}
> > +	trace_i915_request_dep_to(to);
> > +	trace_i915_request_dep_from(from);
> 
> Are those two guaranteed to be atomic ie. no other dep_to/dep_from can get
> injected in the middle of them and if so what guarantees that?
>

These are not atomic but in practice I've never seen an out of order
tracepoints.
 
> Actually we had an internal discussion going in November 2019 on these very
> tracepoints which I think was left hanging in the air.
> 
> There I was suggesting you create a single tracepoint in the format of "from
> -> to", so it's clear without any doubt what is going on.
>

Not sure if it worth adding a custom trace point fo rthis.
 
> I also suggested this should out outside the GuC patch since it is backend
> agnostic.

I guess, but it really matter?

> 
> I also asked why only this flavour of dependencies and not all. You said
> this was the handy one for debugging GuC backend issues. I said in that case
> you should name it trace_i915_request_await_request so it is clearer it does
> not cover all dependencies.
>

Can't we look at the code? For kernel dev trace point I don't this it is
to much to ask a developer to grep around the code. Also you likely only
turn these on if you know what you are doing anyways.
 
> As it stands it is a bit misleadingly named, has that question mark around
> atomicity, and also is not GuC specific. So really I wouldn't think it
> passes the bar in the current state.

I'll just delete them.

> Regards,
> 
> Tvrtko
> 
> P.S. Same discussion from 2019 also talked about
> trace_i915_request_guc_submit and how it exactly aligns to existing request
> in tracepoint.

I doesn't align. You literally make the point about how it doesn't align
below.

> You were saying the new one is handy because it corresponds
> with H2G, as the last request_in of the group would trigger it. I was saying
> that then you could either know implicitly last request_in triggers H2G, or
> that you could consider adding explicit H2G tracepoints.

Yes, we have a trace point for every H2G. Again the users of these
tracepoints know what they mean.

Matt

> 
> > +
> >   	/* Couple the dependency tree for PI on this exposed to->fence */
> >   	if (to->engine->sched_engine->schedule) {
> >   		err = i915_sched_node_add_dependency(&to->sched,
> > diff --git a/drivers/gpu/drm/i915/i915_trace.h b/drivers/gpu/drm/i915/i915_trace.h
> > index 6778ad2a14a4..b02d04b6c8f6 100644
> > --- a/drivers/gpu/drm/i915/i915_trace.h
> > +++ b/drivers/gpu/drm/i915/i915_trace.h
> > @@ -794,22 +794,27 @@ DECLARE_EVENT_CLASS(i915_request,
> >   	    TP_STRUCT__entry(
> >   			     __field(u32, dev)
> >   			     __field(u64, ctx)
> > +			     __field(u32, guc_id)
> >   			     __field(u16, class)
> >   			     __field(u16, instance)
> >   			     __field(u32, seqno)
> > +			     __field(u32, tail)
> >   			     ),
> >   	    TP_fast_assign(
> >   			   __entry->dev = rq->engine->i915->drm.primary->index;
> >   			   __entry->class = rq->engine->uabi_class;
> >   			   __entry->instance = rq->engine->uabi_instance;
> > +			   __entry->guc_id = rq->context->guc_id;
> >   			   __entry->ctx = rq->fence.context;
> >   			   __entry->seqno = rq->fence.seqno;
> > +			   __entry->tail = rq->tail;
> >   			   ),
> > -	    TP_printk("dev=%u, engine=%u:%u, ctx=%llu, seqno=%u",
> > +	    TP_printk("dev=%u, engine=%u:%u, guc_id=%u, ctx=%llu, seqno=%u, tail=%u",
> >   		      __entry->dev, __entry->class, __entry->instance,
> > -		      __entry->ctx, __entry->seqno)
> > +		      __entry->guc_id, __entry->ctx, __entry->seqno,
> > +		      __entry->tail)
> >   );
> >   DEFINE_EVENT(i915_request, i915_request_add,
> > @@ -818,6 +823,21 @@ DEFINE_EVENT(i915_request, i915_request_add,
> >   );
> >   #if defined(CONFIG_DRM_I915_LOW_LEVEL_TRACEPOINTS)
> > +DEFINE_EVENT(i915_request, i915_request_dep_to,
> > +	     TP_PROTO(struct i915_request *rq),
> > +	     TP_ARGS(rq)
> > +);
> > +
> > +DEFINE_EVENT(i915_request, i915_request_dep_from,
> > +	     TP_PROTO(struct i915_request *rq),
> > +	     TP_ARGS(rq)
> > +);
> > +
> > +DEFINE_EVENT(i915_request, i915_request_guc_submit,
> > +	     TP_PROTO(struct i915_request *rq),
> > +	     TP_ARGS(rq)
> > +);
> > +
> >   DEFINE_EVENT(i915_request, i915_request_submit,
> >   	     TP_PROTO(struct i915_request *rq),
> >   	     TP_ARGS(rq)
> > @@ -887,6 +907,21 @@ TRACE_EVENT(i915_request_out,
> >   #else
> >   #if !defined(TRACE_HEADER_MULTI_READ)
> > +static inline void
> > +trace_i915_request_dep_to(struct i915_request *rq)
> > +{
> > +}
> > +
> > +static inline void
> > +trace_i915_request_dep_from(struct i915_request *rq)
> > +{
> > +}
> > +
> > +static inline void
> > +trace_i915_request_guc_submit(struct i915_request *rq)
> > +{
> > +}
> > +
> >   static inline void
> >   trace_i915_request_submit(struct i915_request *rq)
> >   {
> > 
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