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

[Gabriel Krisman Bertazi <krisman@suse.de>]

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?

-- 
Gabriel Krisman Bertazi