chungwong
I have a library which is written in C++, and I wrote a NIF “bridge” for it.
When I bench marked the library in C++, it had ~400-600 ips.
Then I bench marked it in Elixir, the result surprised me and it reached minimum 4k ips.
I couldn’t believe my eyes so I spinning a drogon http server to battle with Phoenix.
And the results from the two stay pretty much the same ~400 rps vs ~3k-6k rps.
How come a native C++ call is MUCH slower than the one from Elixir NIF?
Where Next?
Trending in Questions
Other Trending Topics
Latest on Elixir Forum
Sponsor Spotlight
Master modern tools, write cleaner code, and tackle real-world challenges with Manning books, videos, and courses. Start building today.
Categories:
Sub Categories:
Forums
Popular Tags
- #ecto
- #liveview
- #troubleshooting
- #learning-elixir
- #library
- #deployment
- #erlang
- #testing
- #genserver
- #mix
- #absinthe
- #remote-other
- #otp
- #plug
- #how-to-question
- #macros
- #postgres
- #elixirconf
- #channels
- #exunit
- #discussion
- #code-sync
- #podcasts
- #javascript
- #onsite
- #dialyzer
- #docker
- #authentication
- #umbrella
- #full-time-contract
- #podcasts-by-brainlid
- #ai
- #ecto-query
- #elixirconf-us
- #blog-post
- #elixir-ls
- #phoenix_html
- #iex
- #graphql
- #genstage
- #websockets
- #supervisor
- #advent-of-code
- #distillery
- #processes
- #elixirconf-eu
- #api
- #forms
- #metaprogramming
- #hex
Our Sponsors
Build Elixir applications with speed and confidence.
Supporting innovation across the BEAM ecosystem.
We build reliable cloud platforms for business-critical systems.
Catch errors, track performance, monitor hosts and more.
Elixir, Erlang & BEAM conferences from Code Sync - join us in 2026!
Practical resources that improve the lives of professional developers.
Master modern tools, write cleaner code, and tackle real-world challenges.
Bringing learning, work and compliance together since 1987.
The team behind Membrane, Popcorn, LiveDebugger. Available for hire.
Courses that'll move you from confusion to "Aha, now I get it!"
Showing Posts 1 to 9- Show Best Posts
- Show All (oldest first)
- Show All (newest first)
rjk
Are you able to share the code? It would be easier this way to say something sensible about it.
But from my own experience it’s quite difficult to measure between 2 platforms in a correct way.
(I’m using rustler myself and performance seems to be faster on the 100% rust side, I have never seen the elixir/NIF part being faster because of the (sometimes little) overhead crossing the NIF bridge)
yurko
Could be that your benchmarks are parallelized for BEAM but not when testing native C++?
lukaszsamson
Is it a normal or a dirty NIF? If it is dirty then is the workload IO or CPU bound and is the appropriate flag used in NIF declaration? If It is dirty then does Beam have enough dirty threads set in config (the defaults are rather low)
NobbZ
The problem is not that the BEAM were to “slow”, it is to “fast” compared with the pure C++ benchmark.
It gets about 5 to 10 times as meany IPS in the BEAM when called as NIF compared with the pure C++ benchmark.
hauleth
As @rjk and @yurko said, it can depend on many things. If you could provide MCVE so we could check this out, then maybe we could give you more correct answer.
chungwong
I have made a simplified version of the code.
https://github.com/chungwong/ex_nif
After considering parallel execution and some tweak to C++ compilation,
Parallel 1 in Benchee is around 2.3k IPS and Native C++ is about 2k or so, so they are similar now.
But I still feel Elixir NIF is faster.
hauleth
Pure C++ is 174.96 ns per iteration while Elixir NIF is 423.47 μs, so pure C++ is 2420x faster than Elixir NIF.
chungwong
What about the the IPS? Elixir has higher value.
hauleth
20’000 iterations in 20 seconds mean less throughput than 2’000 iterations in 1 second. And from what I see Google Bench gives you amount of iterations, not IPS.