Maybe this will help How to scrape grafana internal metrics with prometheus
I had a quick look at our Grafana and the link above seems to have the correct info
# curl http://localhost:8080/metrics
# HELP go_gc_duration_seconds A summary of the GC invocation durations.
# TYPE go_gc_duration_seconds summary
go_gc_duration_seconds{quantile="0"} 2.1466e-05
go_gc_duration_seconds{quantile="0.25"} 4.9953e-05
go_gc_duration_seconds{quantile="0.5"} 7.1067e-05
go_gc_duration_seconds{quantile="0.75"} 9.9476e-05
go_gc_duration_seconds{quantile="1"} 0.002339865
go_gc_duration_seconds_sum 1.2995778150000001
go_gc_duration_seconds_count 15677
...