io_uring

io_uring (previously known as aioring) is a Linux kernel system call interface for storage device asynchronous I/O operations addressing performance issues with similar interfaces provided by functions like read()/write() or aio_read()/aio_write() etc. for operations on data accessed by file descriptors.[1][2]: 2 

Development is ongoing, worked on primarily by Jens Axboe at Meta.[1]

Interface

It works by creating two circular buffers, called "queue rings", for storage of submission and completion of I/O requests, respectively. For storage devices, these are called the submission queue (SQ) and completion queue (CQ).[3] Keeping these buffers shared between the kernel and application helps to boost the I/O performance by eliminating the need to issue extra and expensive system calls to copy these buffers between the two.[1][4][3] According to the io_uring design paper, the SQ buffer is writable only by consumer applications, and the CQ buffer is writable only by the kernel.[1]: 3 

eBPF can be combined with io_uring.[5]

History

The kernel interface was adopted in Linux kernel version 5.1.[1][4][6] The liburing library provides an API to interact with the kernel interface easily from userspace.[1][1]: 12  The Linux kernel has supported asynchronous I/O since version 2.5, but it was seen as difficult to use and inefficient.[7] This older API only supported certain niche use cases.[8]

References
  1. "Linux Kernel Getting io_uring To Deliver Fast & Efficient I/O - Phoronix". Phoronix. Retrieved 2021-03-14.{{cite web}}: CS1 maint: url-status (link)
  2. Axboe, Jens (October 15, 2019). "Efficient IO with io_uring" (PDF).{{cite web}}: CS1 maint: url-status (link)
  3. "Getting Hands-on with io_uring using Go". developers.mattermost.com. Retrieved 2021-11-20.
  4. "The rapid growth of io_uring [LWN.net]". lwn.net. Retrieved 2021-11-20.
  5. "BPF meets io_uring [LWN.net]". LWN.net. Retrieved 2023-04-17.
  6. "Faster IO through io_uring | Kernel Recipes 2019". Retrieved 2021-03-14.
  7. Corbet, Jonathan. "Ringing in a new asynchronous I/O API". LWN.net. Retrieved 2021-03-14.{{cite web}}: CS1 maint: url-status (link)
  8. "What's new with io_uring" (PDF). Retrieved 2022-06-01.
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