From 5247c034a67f5a93cc1faa15e9867eec5b22f38a Mon Sep 17 00:00:00 2001 From: Pavel Begunkov Date: Tue, 20 Jan 2026 20:47:40 +0000 Subject: io_uring: introduce non-circular SQ 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. Signed-off-by: Pavel Begunkov Signed-off-by: Jens Axboe --- include/uapi/linux/io_uring.h | 12 ++++++++++++ 1 file changed, 12 insertions(+) (limited to 'include/uapi/linux') diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h index b5b23c0d5283..475094c7a668 100644 --- a/include/uapi/linux/io_uring.h +++ b/include/uapi/linux/io_uring.h @@ -237,6 +237,18 @@ enum io_uring_sqe_flags_bit { */ #define IORING_SETUP_SQE_MIXED (1U << 19) +/* + * When set, io_uring ignores SQ head and tail and fetches SQEs to submit + * starting from index 0 instead from the index stored in the head pointer. + * IOW, the user should place all SQE at the beginning of the SQ memory + * before issuing a submission syscall. + * + * It requires IORING_SETUP_NO_SQARRAY and is incompatible with + * IORING_SETUP_SQPOLL. The user must also never change the SQ head and tail + * values and keep it set to 0. Any other value is undefined behaviour. + */ +#define IORING_SETUP_SQ_REWIND (1U << 20) + enum io_uring_op { IORING_OP_NOP, IORING_OP_READV, -- cgit v1.2.3