[PATCH 10/16] io_uring: static_key for !IORING_SETUP_NO_SQARRAY

[Pavel Begunkov <asml.silence@gmail.com>]

At some point IORING_SETUP_NO_SQARRAY should become the default, so add
a static_key to optimise out the chunk of io_get_sqe() dealing with
sq_arrays.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 io_uring/io_uring.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index ac6d1687ba6c..c39606740c73 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -72,6 +72,7 @@
 #include <linux/io_uring.h>
 #include <linux/audit.h>
 #include <linux/security.h>
+#include <linux/jump_label.h>
 #include <asm/shmparam.h>
 
 #define CREATE_TRACE_POINTS
@@ -148,6 +149,8 @@ static bool io_uring_try_cancel_requests(struct io_ring_ctx *ctx,
 
 static void io_queue_sqe(struct io_kiocb *req);
 
+static __read_mostly DEFINE_STATIC_KEY_FALSE(io_key_has_sqarray);
+
 struct kmem_cache *req_cachep;
 
 struct sock *io_uring_get_socket(struct file *file)
@@ -2342,7 +2345,8 @@ static bool io_get_sqe(struct io_ring_ctx *ctx, const struct io_uring_sqe **sqe)
 	unsigned mask = ctx->sq_entries - 1;
 	unsigned head = ctx->cached_sq_head++ & mask;
 
-	if (!(ctx->flags & IORING_SETUP_NO_SQARRAY)) {
+	if (static_branch_unlikely(&io_key_has_sqarray) &&
+	    (!(ctx->flags & IORING_SETUP_NO_SQARRAY))) {
 		head = READ_ONCE(ctx->sq_array[head]);
 		if (unlikely(head >= ctx->sq_entries)) {
 			/* drop invalid entries */
@@ -2871,6 +2875,9 @@ static __cold void io_ring_ctx_free(struct io_ring_ctx *ctx)
 #endif
 	WARN_ON_ONCE(!list_empty(&ctx->ltimeout_list));
 
+	if (!(ctx->flags & IORING_SETUP_NO_SQARRAY))
+		static_branch_dec(&io_key_has_sqarray);
+
 	io_alloc_cache_free(&ctx->rsrc_node_cache, io_rsrc_node_cache_free);
 	if (ctx->mm_account) {
 		mmdrop(ctx->mm_account);
@@ -3844,6 +3851,9 @@ static __cold int io_uring_create(unsigned entries, struct io_uring_params *p,
 	if (!ctx)
 		return -ENOMEM;
 
+	if (!(ctx->flags & IORING_SETUP_NO_SQARRAY))
+		static_branch_inc(&io_key_has_sqarray);
+
 	if ((ctx->flags & IORING_SETUP_DEFER_TASKRUN) &&
 	    !(ctx->flags & IORING_SETUP_IOPOLL) &&
 	    !(ctx->flags & IORING_SETUP_SQPOLL))
-- 
2.41.0