Re: [PATCH 0/4] implement vectored registered buffers for sendzc

[Jens Axboe <axboe@kernel.dk>]

On 10/22/24 8:38 PM, Pavel Begunkov wrote:
> Allow registered buffers to be used with zerocopy sendmsg, where the
> passed iovec becomes a scatter list into the registered buffer
> specified by sqe->buf_index. See patches 3 and 4 for more details.
> 
> To get performance out of it, it'll need a bit more work on top for
> optimising allocations and cleaning up send setups. We can also
> implement it for non zerocopy variants and reads/writes in the future.
> 
> Tested by enabling it in test/send-zerocopy.c, which checks payloads,
> and exercises lots of corner cases, especially around send sizes,
> offsets and non aligned registered buffers.

Just for the edification of the list readers, Pavel and I discussed this
a bit last night. There's a decent amount of overlap with the send zc
provided + registered buffers work that I did last week, but haven't
posted yet. It's here;

https://git.kernel.dk/cgit/linux/log/?h=io_uring-sendzc-provided

in terms of needing and using both bvec and iovec in the array, and
having the suitable caching for the arrays rather than needing a full
alloc + free every time.

The send zc part can map into bvecs upfront and hence don't need the
iovec array storage at the same time, which this one does as the sendmsg
zc opcode needs to import an iovec. But perhaps there's a way to still
unify the storage and retain the caching, without needing to come up
with something new.

Just a brief summary of the out-of-band discussion.

-- 
Jens Axboe