usrbio engine for fio (#62)

* usrbio engine for fio

* Update README.md

benchmarks/fio_usrbio/README.md

@@ -0,0 +1,35 @@
+# FIO engine for 3FS USRBIO
+
+This repository contains the [fio] external plugin used for benchmarking [3FS] USRBIO.
+
+## Build
+
+First, build 3FS and fio.
+
+Configure the following variables:
+- `HF3FS_LIB_DIR`: directory contains `libhf3fs_api_shared.so`, the default path in 3FS repo is `3FS/build/src/lib/api`.
+- `HF3FS_INCLUDE_DIR`: directory contains `hf3fs_usrbio.h`, the default path in 3FS repo is `3FS/src/lib/api`.
+- `FIO_SRC_DIR`: directory contains `config-host.h`. After building fio, this header will be in the root of the fio repo.
+
+Then run:
+```
+make HF3FS_LIB_DIR=${HF3FS_LIB_DIR} HF3FS_INCLUDE_DIR=${HF3FS_INCLUDE_DIR} FIO_SRC_DIR=${FIO_SRC_DIR}
+```
+
+You will get the external plugin as `hf3fs_usrbio.so`.
+
+## Usage
+
+To use this plugin, set the `ioengine` args in fio as `external:hf3fs_usrbio.so`. Please refer to [fio documentation] for further explanation.
+
+To benchmarking batched small I/Os, please set these four parameters to `batch_size` simultaneously:
+```
+iodepth=1024
+iodepth_batch_submit=1024
+iodepth_batch_complete_min=1024
+iodepth_batch_complete_max=1024
+```
+
+[fio]: https://github.com/axboe/fio
+[3FS]: https://github.com/deepseek-ai/3FS
+[fio documentation]: https://fio.readthedocs.io/en/latest/fio_doc.html