Re: [PATCH v3 1/1] io_uring: introduce non-circular SQ

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

On 1/21/26 18:20, Gabriel Krisman Bertazi wrote:
> Pavel Begunkov <asml.silence@gmail.com> writes:
> 
>> Outside of SQPOLL, normally SQ entries are consumed by the time the
>> submission syscall returns. For those cases we don't need a circular
>> buffer and the head/tail tracking, instead the kernel can assume that
>> entries always start from the beginning of the SQ at index 0. This patch
>> introduces a setup flag doing exactly that. It's a simpler and helps
>> to keeps SQEs hot in cache.
>>
>> The feature is optional and enabled by setting IORING_SETUP_SQ_REWIND.
>> The flag is rejected if passed together with SQPOLL as it'd require
>> waiting for SQ before each submission. It also requires
>> IORING_SETUP_NO_SQARRAY, which can be supported but it's unlikely there
>> will be users, so leave more space for future optimisations.
> 
> This patch got me wondering if it would make sense to have a way to
> point to different buffers as the SQE map and execute them.  This way
> the user could initialize a set of operations in a specific region of
> the sq ring (or a separate buffer) once and have them repeatedly
> executed with a single command, similar to a procedure call.
> 
> Say we have a preloaded ring with some sqes to accept a new connection,
> and immediately some fixed data, etc.  When I want to run it, I push a
> SQE OP_EXECUTE pointing to this buffer to the "main" ring and io_uring
> will queue everything in this pre-registered buffer.
> 
> I imagine it would save nothing beyond SQ initialization. just curious
> if you see a use case for something like this?

You already can do it with the sq array. Never heard of anyone
using it, but liburing never exposed it to users either.

-- 
Pavel Begunkov