1. How does ROMIO implement asynchronous I/O? I mean do you use POSIX-AIO, native Linux kernel AIO (io_submit,..),  io_uring, or anything else? If I debug my code at our Clusters with gdb, I can see that POSIX-AIO is used. But is this on all systems so?
2. When and how does asynchronous I/O progress occur? Do you span multiple I/O threads for a rank? Is this related to variable MPICH_ASYNC_PROGRESS? Again with gdb, I can see that several asynchronous write requests by the same MPI rank are handled successively by a single thread.   
   
3. Is there any related recent publication is can use to cite? I didn't find anything related to the implementation of asynchronous MPI-IO, except this: https://web.cels.anl.gov/~thakur/papers/grequest-redesign.pdf. But is it not outdated?
   

Best regards,

Ahmad