io_uring: move multishot cqe cache in ctx

We cache multishot CQEs before flushing them to the CQ in
submit_state.cqe. It's a 16 entry cache totalling 256 bytes in the
middle of the io_submit_state structure. Move it out of there, it
should help with CPU caches for the submission state, and shouldn't
affect cached CQEs.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/dbe1f39c043ee23da918836be44fcec252ce6711.1692916914.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: isilence

include/linux/io_uring_types.h

@@ -176,7 +176,6 @@ struct io_submit_state {
 	unsigned short		submit_nr;
 	unsigned int		cqes_count;
 	struct blk_plug		plug;
-	struct io_uring_cqe	cqes[16];
 };
 
 struct io_ev_fd {
@@ -307,6 +306,8 @@ struct io_ring_ctx {
 		unsigned		cq_last_tm_flush;
 	} ____cacheline_aligned_in_smp;
 
+	struct io_uring_cqe	completion_cqes[16];
+
 	/* IRQ completion list, under ->completion_lock */
 	struct io_wq_work_list	locked_free_list;
 	unsigned int		locked_free_nr;

io_uring/io_uring.c

@@ -880,7 +880,7 @@ static void __io_flush_post_cqes(struct io_ring_ctx *ctx)
 
 	lockdep_assert_held(&ctx->uring_lock);
 	for (i = 0; i < state->cqes_count; i++) {
-		struct io_uring_cqe *cqe = &state->cqes[i];
+		struct io_uring_cqe *cqe = &ctx->completion_cqes[i];
 
 		if (!io_fill_cqe_aux(ctx, cqe->user_data, cqe->res, cqe->flags)) {
 			if (ctx->task_complete) {
@@ -931,7 +931,7 @@ bool io_fill_cqe_req_aux(struct io_kiocb *req, bool defer, s32 res, u32 cflags)
 
 	lockdep_assert_held(&ctx->uring_lock);
 
-	if (ctx->submit_state.cqes_count == ARRAY_SIZE(ctx->submit_state.cqes)) {
+	if (ctx->submit_state.cqes_count == ARRAY_SIZE(ctx->completion_cqes)) {
 		__io_cq_lock(ctx);
 		__io_flush_post_cqes(ctx);
 		/* no need to flush - flush is deferred */
@@ -945,7 +945,7 @@ bool io_fill_cqe_req_aux(struct io_kiocb *req, bool defer, s32 res, u32 cflags)
 	if (test_bit(IO_CHECK_CQ_OVERFLOW_BIT, &ctx->check_cq))
 		return false;
 
-	cqe = &ctx->submit_state.cqes[ctx->submit_state.cqes_count++];
+	cqe = &ctx->completion_cqes[ctx->submit_state.cqes_count++];
 	cqe->user_data = user_data;
 	cqe->res = res;
 	cqe->flags = cflags;