io_uring: restructure submit sqes to_submit checks

Put an explicit check for number of requests to submit. First,
we can turn while into do-while and it generates better code, and second
that if can be cheaper, e.g. by using CPU flags after sub in
io_sqring_entries().

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/5926baadd20c28feab7a5e1725fedf32e4553ff7.1632516769.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/fs/io_uring.c b/fs/io_uring.c
index bbb2a26..b8f60cf 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -7225,16 +7225,19 @@ static const struct io_uring_sqe *io_get_sqe(struct io_ring_ctx *ctx)
 static int io_submit_sqes(struct io_ring_ctx *ctx, unsigned int nr)
        __must_hold(&ctx->uring_lock)
 {
+       unsigned int entries = io_sqring_entries(ctx);
        int submitted = 0;
 
+       if (!entries)
+               return 0;
        /* make sure SQ entry isn't read before tail */
-       nr = min3(nr, ctx->sq_entries, io_sqring_entries(ctx));
+       nr = min3(nr, ctx->sq_entries, entries);
        if (!percpu_ref_tryget_many(&ctx->refs, nr))
                return -EAGAIN;
        io_get_task_refs(nr);
 
        io_submit_state_start(&ctx->submit_state, nr);
-       while (submitted < nr) {
+       do {
                const struct io_uring_sqe *sqe;
                struct io_kiocb *req;
 
@@ -7253,7 +7256,7 @@ static int io_submit_sqes(struct io_ring_ctx *ctx, unsigned int nr)
                submitted++;
                if (io_submit_sqe(ctx, req, sqe))
                        break;
-       }
+       } while (submitted < nr);
 
        if (unlikely(submitted != nr)) {
                int ref_used = (submitted == -EAGAIN) ? 0 : submitted;