问题
I'm trying to use async io on linux. As far as i know there're 3 options:
- kernel calls (io_submit and friends)
- libRT - uses threads in user space
- libRTKAIO - wrapper of kernel calls which does not use threads
I'm using the last option, and i see, that in my unit test that runs a lot of async io requests in multiple threads, /proc/sys/fs/aio-nr is never higher than 1024. I wonder where lays such limitation.
I've set /proc/sys/fs/aio-max-nr to 16M, so it's not an issue.
A related question (also mine) aio_write on linux with rtkaio is sometimes long
回答1:
There's a system call named "io_setup". In librtkaio this call is receiving 1024 as an argument. This, leads to the constant 1024 as i described and hurts performance if there're more than 1024 ios in parallel. Note that 1024 is hardcoded.
Only calling lio_listio in blocking mode will allow you to raise this 1024 bar.
来源：https://stackoverflow.com/questions/1799537/proc-sys-fs-aio-nr-is-never-higher-than-1024-aio-on-linux