This application measures the software overhead of I/O submission
and completion for both the SPDK NVMe driver and an AIO file handle.
It runs a random read, queue depth = 1 workload to a single device,
and captures TSC as follows:
* Submission: capture TSC before and after the I/O submission
call (SPDK or AIO).
* Completion: capture TSC before and after the I/O completion
check. Only record the TSC delta if the I/O completion check
resulted in a completed I/O. Also use heuristics in the AIO
case to account for time spent in interrupt handling outside
of the actual I/O completion check.
Usage:
To test software overhead for a 4KB I/O over a 10 second period:
SPDK: overhead -s 4096 -t 10
AIO: overhead -s 4096 -t 10 /dev/nvme0n1
Note that for the SPDK case, it will only use the first namespace
on the first controller found by SPDK. If a different namespace is
desired, attach controllers individually to the kernel NVMe driver
to ensure they will not be enumerated by SPDK.
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