Notices by Jens Axboe (axboe@fosstodon.org)

@torvalds Yep, we certainly could do that. I did that in io_uring, I'd be weary of doing it generically without auditing all the callers. Some callers assume you'll get an ITER_IOVEC out of those helpers, would make me nervous to do it wholesale inside the functions.

For liburing specifically, I'd want to add a patch that just turns io_uring_prep_{readv,writev} into read/write instead. Because the iovec copy overhead is noticeable too, and the ITER_UBUF conversion only saves iterator overhead.

@torvalds My kvm boots fine with:

diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 274014e4eafe..06e46530cb3d 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -1868,7 +1868,7 @@ int import_single_range(int rw, void __user *buf, size_t len,

iov->iov_base = buf;
iov->iov_len = len;
- iov_iter_init(i, rw, iov, 1, len);
+ iov_iter_ubuf(i, rw, buf, len);
return 0;
}
EXPORT_SYMBOL(import_single_range);

Let me try the __import_iovec() as well...

One of my pet peeves - people using vectored IO operations with single segments. At least now we'll make it a bit better, though still wasting time on copying in a single iovec.

https://lore.kernel.org/io-uring/43cb1fb7-b30b-8df1-bba6-e50797d680c6@kernel.dk/

First cut at the "io_uring and networking in 2023" is now available below. It attempts to highlight some of the features and optimizations that were specifically tailored for networking workloads:

https://kernel.dk/io_uring%20and%20networking%20in%202023.pdf

Feedback welcome!

If PDFs isn't your thing, I also made an attempt at putting it on the github wiki:

https://github.com/axboe/liburing/wiki/io_uring-and-networking-in-2023