Linux AIO: Poor Scaling

Question

I am writing a library that uses the Linux asynchronous I/O system calls, and would like to know why the io_submit function is exhibiting poor scaling on the ext4 f

Answer 1

My understanding is that very few (if any) filesystems on linux fully supports AIO. Some filesystem operations still block, and sometimes io_submit() will, indirectly via filesystem operations, invoke such blocking calls.

My understanding is further that the main users of kernel AIO primarily care about AIO being truly asynchronous on raw block devices (i.e. no filesystem). essentially database vendors.

Here's a relevant post from the linux-aio mailing list. (head of the thread)

A possibly useful recommendation:

Add more requests via /sys/block/xxx/queue/nr_requests and the problem will get better.