Asynchronous I/O Stack: A Low-latency Kernel I/O Stack for Ultra-Low Latency SSDs


Gyusun Lee, Seokha Shin, and Wonsuk Song, Sungkyunkwan University; Tae Jun Ham and Jae W. Lee, Seoul National University; Jinkyu Jeong, Sungkyunkwan University


Today's ultra-low latency SSDs can deliver an I/O latency of sub-ten microseconds. With this dramatically shrunken device time, operations inside the kernel I/O stack, which were traditionally considered lightweight, are no longer a negligible portion. This motivates us to reexamine the storage I/O stack design and propose an asynchronous I/O stack (AIOS), where synchronous operations in the I/O path are replaced by asynchronous ones to overlap I/O-related CPU operations with device I/O. The asynchronous I/O stack leverages a lightweight block layer specialized for NVMe SSDs using the page cache without block I/O scheduling and merging, thereby reducing the sojourn time in the block layer. We prototype the proposed asynchronous I/O stack on the Linux kernel and evaluate it with various workloads. Synthetic FIO benchmarks demonstrate that the application-perceived I/O latency falls into single-digit microseconds for 4 KB random reads on Optane SSD, and the overall I/O latency is reduced by 15-33% across varying block sizes. This I/O latency reduction leads to a significant performance improvement of real-world applications as well: 11-44% IOPS increase on RocksDB and 15-30% throughput improvement on Filebench and OLTP workloads.

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@inproceedings {234934,
author = {Gyusun Lee and Seokha Shin and Wonsuk Song and Tae Jun Ham and Jae W. Lee and Jinkyu Jeong},
title = {Asynchronous {I/O} Stack: A Low-latency Kernel {I/O} Stack for {Ultra-Low} Latency {SSDs}},
booktitle = {2019 USENIX Annual Technical Conference (USENIX ATC 19)},
year = {2019},
isbn = {978-1-939133-03-8},
address = {Renton, WA},
pages = {603--616},
url = {},
publisher = {USENIX Association},
month = jul

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