code: func (t *tracker) start(ctx context.Context, startSpan bool) context.Context {
  	t.startedAt = time.Now()
  
  	ctx, _ = tag.New(ctx, tag.Upsert(Service, t.service), tag.Upsert(Endpoint, t.method))
  	stats.Record(ctx, t.profile.CountMeasure.M(1))
  
  	if startSpan {
  		ctx, t.span = trace.StartSpan(
  			ctx,
  			fmt.Sprintf("rpc/%s/%s/%s", t.profile.Role, t.service, t.method),
  		)
  	}
  
  	return ctx
  }
docs: // start monitoring a request. You can choose to let this method
  // start a span for the request or attach one later.