linux kernel aio functionality

Question

I am testing kernel asynchronous io functions (not posix aio) and am trying to figure out how it works. The code below is a complete program where I simply write an array re

Answer 1

First of all, good job using libaio instead of POSIX aio.

Are there any restrictions on the usage of O_DIRECT ?

I'm not 100% sure this is the real problem, but O_DIRECT has some requirements (quoting mostly from TLPI):

• The data buffer being transferred must be aligned on a memory boundary that is a multiple of the block size (use posix_memalign)
• The file or device offset at which data transfer commences must be a multiple of the block size
• The length of the data to be transferred must be a multiple of the block size

At a glance, I can see you are not taking aby precautions to align memory in allocate_2D_matrix.

If I do not open the file using O_DIRECT, things work fine, but it beats the purpose of having async writes.

This happens not to be the case. Asynchronous I/O works well without O_DIRECT (for instance think of the number of system calls slashed).