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io_uring: optimise submission left counting

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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>
This commit is contained in:
Pavel Begunkov 2022-04-12 15:09:50 +01:00 committed by Jens Axboe
parent 8e6971a819
commit 1cd15904b6
1 changed files with 10 additions and 10 deletions
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20
fs/io_uring.c
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@ -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;