Io uring and xdp enter 2024: Difference between revisions
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Last year (2023), I spent significant time writing code using [[XDP]] and [[io_uring]]. The latter was delightful, the former less so | '''[[Dankblog|dankblog!]] 2024-02-15, 1452 EST, at [[Viewpoint|the danktower]]''' | ||
Last year (2023), I spent significant time writing code using [[XDP]] and [[io_uring]]. The latter was delightful, the former less so. Work on these technologies has progressed, and it seems time for an update. | |||
==XDP== | ==XDP== | ||
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I used to have the following on my io_uring page: | I used to have the following on my io_uring page: | ||
It would be nice to have tight integration with condition variables or even mutex/futex (allow me to submit a request to get a lock, and when i get the CQE, i have that lock). Bonus points if the fast (uncontended) path never needs a system call (like mutexes built atop futexes today). | <q>It would be nice to have tight integration with condition variables or even mutex/futex (allow me to submit a request to get a lock, and when i get the CQE, i have that lock). Bonus points if the fast (uncontended) path never needs a system call (like mutexes built atop futexes today).</q> | ||
The new API appears to satisfy all my desires! | The new API appears to satisfy all my desires! | ||
Also new is <tt>IORING_OP_WAITID</tt> for working with process state changes (though I would recommend use of [[pidfd|pidfds]] for this kind of thing in new code). | Also new is <tt>IORING_OP_WAITID</tt> for working with process state changes (though I would recommend use of [[pidfd|pidfds]] for this kind of thing in new code). | ||
[https://git.kernel.dk/cgit/linux/commit/?h=io_uring-send-queue&id=060845d3788f20b427631b64a6dbdbd249a0309b Kernel 6.8] introduces <tt>IORING_SEND_MULTISHOT</tt>, bringing the multishot pattern to the TX (<tt>send</tt> and <tt>sendmsg</tt>) side. See Axboe's "[https://lore.kernel.org/io-uring/20240308235045.1014125-1-axboe@kernel.dk/ Send and receive bundles]" post for further optimization using "bundles" (these require registered buffers). | |||
<tt>IORING_SETUP_REGISTERED_FD_ONLY</tt> registers the ring fd for use with <tt>IORING_REGISTER_USE_REGISTERED_RING</tt>. | |||
<tt>io_uring_prep_cmd_sock(2)</tt> configures <tt>IORING_OP_URING_CMD</tt> SQEs to perform <tt>setsockopt(2)</tt> operations. | |||
<tt>io_uring_prep_getxattr(2)</tt> and <tt>io_uring_prep_setxattr(2)</tt> prep SQEs for <tt>getxattr(2)</tt> and <tt>setxattr(2)</tt> operations; <tt>io_uring_prep_fgetxattr(2)</tt> and <tt>io_uring_prep_fsetxattr(2)</tt> do exactly what you'd think. | |||
Making huge pages as unpleasant as possible to use is a central tenet (perhaps <i>the</i> central tenet) underpinning the entire Linux mission, but <tt>IORING_SETUP_NO_MMAP</tt> was [https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=03d89a2de25b added in 6.5], huzzah! | |||
==See also== | ==See also== | ||
* [https://elixir.bootlin.com/linux/latest/source/Documentation/networking/af_xdp.rst AF_XDP] kernel documentation | * [https://elixir.bootlin.com/linux/latest/source/Documentation/networking/af_xdp.rst AF_XDP] kernel documentation | ||
'''previously: "[[Ebooks_are_hot_garbage|ebooks are hot garbage]]" 2024-02-11''' | |||
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