fio IO Engine#

The xNVMe fio IO engine is provided with upstream fio. A nice introduction to using it is provided by Vincent Fu and Ankit Kumar here:

To supplement the above, then a bit of information is provided here on building fio with the xNVMe I/O engine enabled, as well as some known caveats. However, the introduction above is well recommended read.

Enabling the xNVMe engine#

First, consult the Getting Started section, to build and install xNVMe. Then go ahead and build and install fio from source:

#
# Clone, build, configure, and install fio v3.34 with the xNVMe I/O engine
#
# Assumptions:
#
# - xNVMe is installed on the system (the fio build-system picks up xNVMe)
# - These commands are executed with sufficient privileges (sudo/root)
#
git clone https://github.com/axboe/fio.git toolbox/third-party/fio/repository

pushd toolbox/third-party/fio/repository
git checkout fio-3.36
./configure
make -j
make install
popd

That is all there is to it. The fio build-system will automatically detect that xNVMe is installed on the system, link with it, and thereby enable the xNVMe I/O engine.

Note

In case you explicitly do not want fio to look for xNVMe, then you can instruct the fio build-system with ./configure --disable-xnvme. This might be useful when building external I/O engines, such as those provided by SPDK.

Caveats#

This section provides a couple of notes and insights to double check in case you are facing unexpected issues.

Threading vs Forking#

  • Must be used with --thread=1

The above option is required as forking for parallel job execution is not supported; aka threading is required.

Multi-device support#

  • Multiple devices are supported, however, they all either have to be operating-system managed or all utilize a User space driver.

Details follow.

  1. iomem_{alloc/free} introduces a limitation with regards to multiple devices. Specifically, the devices opened must use backends which share memory allocators. E.g. using be:linux + be:posix is fine, using be:linux + be:spdk is not. This is due to the fio ‘io_mem_*’ helpers are not tied to devices, as such, it is required that all devices opened use compatible buffer-allocators. Currently, the implementation does dot check for this unsupported use-case, and will thus lead to a runtime error.

  2. The implementation assumes that thread_data.o.nr_files is available and that instances of fio_file.fileno are valued [0, thread_data.o.nr_files -1]. This is to pre-allocate file-wrapping-structures, xnvme_fioe_fwrap, at I/O engine initialization time and to reference file-wrapping with constant-time lookup.

  3. The _open() and _close() functions do not implement the “real” device/file opening, this is done in _init() and torn down in _cleanup() as the io-engine needs device handles ready for iomem_{alloc/free}.

NVMe devices formatted with extended-LBA#

  • These are currently not supported.

Details follow.

To support extended-lba initial work has been done in xNVMe, however, further work is probably need for this to trickle up to the fio I/O engine, also, in the io-engine >> ssw are used which does not account for extended LBA.

History#

Previously, then the xNVMe IO engine was external. That meant that the engine was built externally from the built of fio itself, and the source-code for the engine was provided with xNVMe.

From fio-v3.32, then xNVMe IO engine became available as an “internal” engine i upstream fio. That meant that the engine was built along with the built of fio itself, and the source-code of the engine is distributed with fio.

From fio-v.34, then all features of the external xNVMe IO engine where upstreamed and removed from the xNVMe repository. xNVMe-v0.6.0 was the last version to ship the external engine.

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