io_uring: optimise plugging

Plugging is only needed with requests that also need a file, so hide
plugging under a ->needs_file check. Also, place ->needs_file and ->plug
bits into the same byte of io_op_defs, it may matter for compilers, e.g.
only with the change a tested one decided to optimise two memory testb
into a more with two register testb.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/1600d1287bb7d16451d4ef3343252787a5314927.1633532552.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 44946711fe62aa924f36d3ccf59de3fa2fa23387..7759fabf9ae017b1cafbdf3d5d054b782af2b2b6 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -894,12 +894,12 @@ struct io_defer_entry {
 struct io_op_def {
        /* needs req->file assigned */
        unsigned                needs_file : 1;
+       /* should block plug */
+       unsigned                plug : 1;
        /* hash wq insertion if file is a regular file */
        unsigned                hash_reg_file : 1;
        /* unbound wq insertion if file is a non-regular file */
        unsigned                unbound_nonreg_file : 1;
-       /* opcode is not supported by this kernel */
-       unsigned                not_supported : 1;
        /* set if opcode supports polled "wait" */
        unsigned                pollin : 1;
        unsigned                pollout : 1;
@@ -907,8 +907,8 @@ struct io_op_def {
        unsigned                buffer_select : 1;
        /* do prep async if is going to be punted */
        unsigned                needs_async_setup : 1;
-       /* should block plug */
-       unsigned                plug : 1;
+       /* opcode is not supported by this kernel */
+       unsigned                not_supported : 1;
        /* size of async data needed, if any */
        unsigned short          async_size;
 };
@@ -6978,7 +6978,6 @@ static int io_init_req(struct io_ring_ctx *ctx, struct io_kiocb *req,
                       const struct io_uring_sqe *sqe)
        __must_hold(&ctx->uring_lock)
 {
-       struct io_submit_state *state;
        unsigned int sqe_flags;
        int personality;
 
@@ -7025,19 +7024,20 @@ static int io_init_req(struct io_ring_ctx *ctx, struct io_kiocb *req,
                get_cred(req->creds);
                req->flags |= REQ_F_CREDS;
        }
-       state = &ctx->submit_state;
-
-       /*
-        * Plug now if we have more than 1 IO left after this, and the target
-        * is potentially a read/write to block based storage.
-        */
-       if (state->need_plug && io_op_defs[req->opcode].plug) {
-               blk_start_plug(&state->plug);
-               state->plug_started = true;
-               state->need_plug = false;
-       }
 
        if (io_op_defs[req->opcode].needs_file) {
+               struct io_submit_state *state = &ctx->submit_state;
+
+               /*
+                * Plug now if we have more than 2 IO left after this, and the
+                * target is potentially a read/write to block based storage.
+                */
+               if (state->need_plug && io_op_defs[req->opcode].plug) {
+                       state->plug_started = true;
+                       state->need_plug = false;
+                       blk_start_plug(&state->plug);
+               }
+
                req->file = io_file_get(ctx, req, READ_ONCE(sqe->fd),
                                        (sqe_flags & IOSQE_FIXED_FILE));
                if (unlikely(!req->file))