Re: [PATCH 0/8] Add support for vectored registered buffers

[Andres Freund <andres@anarazel.de>]

Hi,

On 2025-03-03 15:50:55 +0000, Pavel Begunkov wrote:
> Add registered buffer support for vectored io_uring operations. That
> allows to pass an iovec, all entries of which must belong to and
> point into the same registered buffer specified by sqe->buf_index.

This is very much appreciated!


> The series covers zerocopy sendmsg and reads / writes. Reads and
> writes are implemented as new opcodes, while zerocopy sendmsg
> reuses IORING_RECVSEND_FIXED_BUF for the api.
> 
> Results are aligned to what one would expect from registered buffers:
> 
> t/io_uring + nullblk, single segment 16K:
>   34 -> 46 GiB/s

FWIW, I'd expect bigger wins with real IO when using 1GB huge pages. I
encountered when there were a lot of reads from a large nvme raid into a small
set of shared huge pages (database buffer pool), by many proceses
concurrently. The constant pinning/unpinning of the relevant folio caused a
lot of contention.

Unfortunately switching to registered buffers would, until now, have required
using non-vectored IO, which causes significant performance regressions in
other cases...

Greetings,

Andres Freund