Hey Austin! I realize that making all of the relevant calls to Erlang directly is possible (I might even say straightforward), but the problem is that it's not *discoverable*. The intent here is to 'pave the golden path' and help make the existence and usage of perf_counter clear & straightforward for folks, and to do so in the first place they're likely to look (namely alongside the other `*_time` functions in `System`).
I'm a pretty experienced and extremely curious guy who's been doing this for quite a while, and if `perf_counter` is news to me, it's likely news to a lot of other people as well. The intent of this proposal isn't to make things *possible*, it's to make them *discoverable*. Also, neat context-driven start_span / stop_span model! I've been thinking about something similar for my upcoming telemetry work in Bandit and it's encouraging to see prior art for the idea! m. On Friday, November 4, 2022 at 7:05:50 p.m. UTC-4 halos...@gmail.com wrote: > I just implemented some telemetry in a library that should be usable in > hot paths (but likely has more expensive costs than the telemetry path) and > I didn’t use any of the Elixir wrappers to the Erlang module functions, but > called them directly. > > https://github.com/KineticCafe/app_identity/pull/3 > > Do we need this? > > -a > > On Fri, Nov 4, 2022 at 4:49 PM Mat Trudel <m...@geeky.net> wrote: > >> Using tools such as telemetry in a performant manner requires access to >> some sort of low cost timing primitive to be able to calculate intervals. >> The community seems to use a mixture of `System.system_time/0` and/or >> `System.monotinic_time/0` to accomplish this, though neither of these are >> built specifically for purpose, and neither are terribly performant on >> super hot paths [1]. >> >> As it turns out, Erlang provides a tool for exactly this purpose, though >> Elixir doesn't expose it natively. That tool is `:os.perf_counter/1`: >> https://www.erlang.org/doc/man/os.html#perf_counter-1 >> >> It would be good to have first-class access to this in Elixir. Therefore, >> it is proposed to add the following to System: >> >> * Add `System.perf_counter/0` & `System.perf_counter/1` as thin wrappers >> around `:os.perf_counter`, in the same manner as is currently done for >> `System.system_time` et al >> >> * Add support for `perf_counter` to `System.convert_time_unit/3`. This is >> already supported in the underlying `:erlang.convert_time_unit/3`, it's >> just a matter of adding a clause to the private `normalize_time_unit` >> function. >> >> Combined, these will allow for *significantly* faster interval >> calculation, which should help speed up all sorts of hot telemetry paths. >> >> In practice, `perf_counter` is about twice as fast as `system_time`. A >> quick comparison (run on an M1 MacBook Air running 1.14/OTP 25.1): >> >> ``` >> Mix.install([{:benchee, "~> 1.0", only: :dev}]) >> >> Benchee.run(%{ >> system_time: &System.system_time/0, >> monotonic_time: &System.monotonic_time/0, >> perf_counter: &:os.perf_counter/0 >> }) >> >> Name ips average deviation median >> 99th % >> perf_counter 54.03 M 18.51 ns ±439.35% 18.33 ns >> 20.01 ns >> monotonic_time 28.10 M 35.58 ns ±2758.64% 33.30 ns >> 41.70 ns >> system_time 23.44 M 42.67 ns ±8964.02% 37.50 ns >> 45.90 ns >> >> Comparison: >> perf_counter 54.03 M >> monotonic_time 28.10 M - 1.92x slower +17.08 ns >> system_time 23.44 M - 2.31x slower +24.16 ns >> ``` >> >> If folks are onboard I can get this implemented immediately. >> >> m. >> >> [1] https://github.com/mtrudel/thousand_island/issues/1, among others >> >> -- >> You received this message because you are subscribed to the Google Groups >> "elixir-lang-core" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to elixir-lang-co...@googlegroups.com. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/elixir-lang-core/9d4111e5-4799-4781-bbf1-43dae14dcb94n%40googlegroups.com >> >> <https://groups.google.com/d/msgid/elixir-lang-core/9d4111e5-4799-4781-bbf1-43dae14dcb94n%40googlegroups.com?utm_medium=email&utm_source=footer> >> . >> > > > -- > Austin Ziegler • halos...@gmail.com • aus...@halostatue.ca > http://www.halostatue.ca/ • http://twitter.com/halostatue > -- You received this message because you are subscribed to the Google Groups "elixir-lang-core" group. To unsubscribe from this group and stop receiving emails from it, send an email to elixir-lang-core+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/elixir-lang-core/e9f7df4a-5ee1-4ca3-8111-c9d221ebff75n%40googlegroups.com.
