Re: [PATCHSET v2 RFC 0/11] Add support for ring mapped provided buffers

[Pavel Begunkov <asml.silence@gmail.com>]

On 4/29/22 18:56, Jens Axboe wrote:
> Hi,
> 
> This series builds to adding support for a different way of doing
> provided buffers. The interesting bits here are patch 11, which also has
> some performance numbers an an explanation of it.

Jens, would be great if you can CC me for large changes, you know
how it's with mailing lists nowadays...

1) reading "io_uring: abstract out provided buffer list selection"

Let's move io_ring_submit_unlock() to where the lock call is.
In the end, it's only confusing and duplicates unlock in
io_ring_buffer_select() and io_provided_buffer_select().

2) As it's a new API, let's do bucket selection right, I quite
don't like io_buffer_get_list(). We can replace "bgid" with
indexes into an array and let the userspace to handle indexing.
Most likely it knows the index right away or can implement indexes
lookup with as many tricks and caching it needs.


> Patches 1..5 are cleanups that should just applied separately, I
> think the clean up the existing code quite nicely.
> 
> Patch 6 is a generic optimization for the buffer list lookups.
> 
> Patch 7 adds NOP support for provided buffers, just so that we can
> benchmark the last change.
> 
> Patches 8..10 are prep for patch 11.
> 
> Patch 11 finally adds the feature.
> 
> This passes the full liburing suite - obviously this just means that it
> didn't break anything existing (that I know of), the only test case for
> the ring buffers is the nop peak benchmark referenced in patch 11.
> 
> v2:	- Minor optimizations
> 	- Fix 4k PAGE_SIZE assumption
> 	- Style cleanup
> 
> Can also be found in my git repo, for-5.19/io_uring-pbuf branch:
> 
> https://git.kernel.dk/cgit/linux-block/log/?h=for-5.19/io_uring-pbuf
> 
>   fs/io_uring.c                 | 463 +++++++++++++++++++++++++---------
>   include/uapi/linux/io_uring.h |  26 ++
>   2 files changed, 370 insertions(+), 119 deletions(-)
> 

-- 
Pavel Begunkov