mirror of
https://github.com/torvalds/linux
synced 2024-07-20 18:08:48 +00:00
ac5f71a3d9
It's pretty trivial to wire up provided buffer support for the send side, just like how it's done the receive side. This enables setting up a buffer ring that an application can use to push pending sends to, and then have a send pick a buffer from that ring. One of the challenges with async IO and networking sends is that you can get into reordering conditions if you have more than one inflight at the same time. Consider the following scenario where everything is fine: 1) App queues sendA for socket1 2) App queues sendB for socket1 3) App does io_uring_submit() 4) sendA is issued, completes successfully, posts CQE 5) sendB is issued, completes successfully, posts CQE All is fine. Requests are always issued in-order, and both complete inline as most sends do. However, if we're flooding socket1 with sends, the following could also result from the same sequence: 1) App queues sendA for socket1 2) App queues sendB for socket1 3) App does io_uring_submit() 4) sendA is issued, socket1 is full, poll is armed for retry 5) Space frees up in socket1, this triggers sendA retry via task_work 6) sendB is issued, completes successfully, posts CQE 7) sendA is retried, completes successfully, posts CQE Now we've sent sendB before sendA, which can make things unhappy. If both sendA and sendB had been using provided buffers, then it would look as follows instead: 1) App queues dataA for sendA, queues sendA for socket1 2) App queues dataB for sendB queues sendB for socket1 3) App does io_uring_submit() 4) sendA is issued, socket1 is full, poll is armed for retry 5) Space frees up in socket1, this triggers sendA retry via task_work 6) sendB is issued, picks first buffer (dataA), completes successfully, posts CQE (which says "I sent dataA") 7) sendA is retried, picks first buffer (dataB), completes successfully, posts CQE (which says "I sent dataB") Now we've sent the data in order, and everybody is happy. It's worth noting that this also opens the door for supporting multishot sends, as provided buffers would be a prerequisite for that. Those can trigger either when new buffers are added to the outgoing ring, or (if stalled due to lack of space) when space frees up in the socket. Signed-off-by: Jens Axboe <axboe@kernel.dk> |
||
|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .editorconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.