mt-caret/async_io_uring

io_uring backend for Async. Currently only used for watching file descriptors and very beta; expect lots of crashes.

build instructions (w/ OCaml 4.11.1, YMMV for other versions):

$ git clone --recursive https://github.com/mt-caret/async_io_uring
$ opam install dune dune-configurator ocaml-compiler-libs ocaml-migrate-parsetree octavius stdlib-shims
$ cd async_io_uring/io_uring_test
$ dune build --profile release @@default
$ ASYNC_CONFIG="((file_descr_watcher Io_uring))" ../_build/default/io_uring_test/async_tcp_server.exe

currently, the following libraries have been forked w/ changes:

core
ppx_sexp_conv
ppx_expect
ppx_string
ppx_sexp_message
ppx_custom_printf
ppx_fields_conv
ppx_optcomp
async
async_kernel
async_unix

benchmarks:

currently, Async using the io_uring backend seems to be a bit slower than the epoll backend? tested using the command ab -n 100000 -c 10 http://localhost:8000/.

epoll backend:

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:        0    0   0.0      0       1
Processing:     0    1   1.6      1      21
Waiting:        0    1   1.5      1      21
Total:          0    1   1.6      1      21

Percentage of the requests served within a certain time (ms)
  50%      1
  66%      1
  75%      1
  80%      2
  90%      3
  95%      5
  98%      7
  99%      9
 100%     21 (longest request)

io_uring backend:

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:        0    0   0.0      0       1
Processing:     0    1   1.6      1      28
Waiting:        0    1   1.6      1      28
Total:          0    1   1.6      1      28

Percentage of the requests served within a certain time (ms)
  50%      1
  66%      1
  75%      1
  80%      2
  90%      3
  95%      5
  98%      6
  99%     10
 100%     28 (longest request)

todo:

figure out above benchmarks
- shot in the dark guess: allocation of a list in the critical path is the culprit? possibly return a immediate option?
investigate ETIME in io_uring_peek_cqe()
keep track of the number of in-flight I/O and implement pushback

mt-caret / async_io_uring

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