linux: introduce io_uring support (#3952)

Add io_uring support for several asynchronous file operations:

- read, write
- fsync, fdatasync
- stat, fstat, lstat

io_uring is used when the kernel is new enough, otherwise libuv simply
falls back to the thread pool.

Performance looks great; an 8x increase in throughput has been observed.

This work was sponsored by ISC, the Internet Systems Consortium.

Fixes: https://github.com/libuv/libuv/issues/1947

1 files changed, 6 insertions, 0 deletions

diff --git a/docs/src/fs.rst b/docs/src/fs.rst
index fb27a3b9..e7522d59 100644
--- a/docs/src/fs.rst
+++ b/docs/src/fs.rst
@@ -12,6 +12,12 @@ otherwise it will be performed asynchronously.
 All file operations are run on the threadpool. See :ref:`threadpool` for information
 on the threadpool size.
 
+Starting with libuv v1.45.0, some file operations on Linux are handed off to
+`io_uring <https://en.wikipedia.org/wiki/Io_uring>` when possible. Apart from
+a (sometimes significant) increase in throughput there should be no change in
+observable behavior. Libuv reverts to using its threadpool when the necessary
+kernel features are unavailable or unsuitable.
+
 .. note::
      On Windows `uv_fs_*` functions use utf-8 encoding.