From 1cd15904b6e836f46e925229da8950785252b315 Mon Sep 17 00:00:00 2001
From: Pavel Begunkov <asml.silence@gmail.com>
Date: Tue, 12 Apr 2022 15:09:50 +0100
Subject: [PATCH] io_uring: optimise submission left counting
Git-commit: 1cd15904b6e836f46e925229da8950785252b315
Patch-mainline: v5.19-rc1
References: bsc#1205205
Considering all inlining io_submit_sqe() is huge and usually ends up
calling some other functions.
We decrement @left in io_submit_sqes() just before calling
io_submit_sqe() and use it later after the call. Considering how huge
io_submit_sqe() is, there is not much hope @left will be treated
gracefully by compilers.
Decrement it after the call, not only it's easier on register spilling
and probably saves stack write/read, but also at least for x64 uses
CPU flags set by the dec instead of doing (read/write and tests).
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/807f9a276b54ee8ff4e42e2b78721484f1c71743.1649771823.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Gabriel Krisman Bertazi <krisman@suse.de>
---
fs/io_uring.c | 20 ++++++++++----------
1 file changed, 10 insertions(+), 10 deletions(-)
diff --git a/fs/io_uring.c b/fs/io_uring.c
index 3e84963b14ff..c3cadb36326b 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -7877,17 +7877,17 @@ static int io_submit_sqes(struct io_ring_ctx *ctx, unsigned int nr)
io_req_add_to_cache(req, ctx);
break;
}
- /* will complete beyond this point, count as submitted */
- left--;
- if (io_submit_sqe(ctx, req, sqe)) {
- /*
- * Continue submitting even for sqe failure if the
- * ring was setup with IORING_SETUP_SUBMIT_ALL
- */
- if (!(ctx->flags & IORING_SETUP_SUBMIT_ALL))
- break;
+
+ /*
+ * Continue submitting even for sqe failure if the
+ * ring was setup with IORING_SETUP_SUBMIT_ALL
+ */
+ if (unlikely(io_submit_sqe(ctx, req, sqe)) &&
+ !(ctx->flags & IORING_SETUP_SUBMIT_ALL)) {
+ left--;
+ break;
}
- } while (left);
+ } while (--left);
if (unlikely(left)) {
ret -= left;
--
2.35.3