[PATCH 05/10] io_uring: cache last io_buffer_list lookup

[Jens Axboe <axboe@kernel.dk>]

Most use cases have 1 or few buffer groups, and even if they have
multiple, there's often some locality in looking them up. Add a basic
one-hit cache to avoid hashing the group ID and starting the list
iteration.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/io_uring.c | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 3c46915ebf35..50d48d3e05b7 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -411,14 +411,16 @@ struct io_ring_ctx {
 		struct io_mapped_ubuf	**user_bufs;
 
 		struct io_submit_state	submit_state;
+		struct list_head	*io_buffers;
+		struct io_buffer_list	*io_bl_last;
+		unsigned int		io_bl_bgid;
+		u32			pers_next;
+		struct list_head	io_buffers_cache;
 		struct list_head	timeout_list;
 		struct list_head	ltimeout_list;
 		struct list_head	cq_overflow_list;
-		struct list_head	*io_buffers;
-		struct list_head	io_buffers_cache;
 		struct list_head	apoll_cache;
 		struct xarray		personalities;
-		u32			pers_next;
 		unsigned		sq_thread_idle;
 	} ____cacheline_aligned_in_smp;
 
@@ -1616,10 +1618,17 @@ static struct io_buffer_list *io_buffer_get_list(struct io_ring_ctx *ctx,
 	struct list_head *hash_list;
 	struct io_buffer_list *bl;
 
+	if (bgid == ctx->io_bl_bgid)
+		return ctx->io_bl_last;
+
 	hash_list = &ctx->io_buffers[hash_32(bgid, IO_BUFFERS_HASH_BITS)];
-	list_for_each_entry(bl, hash_list, list)
-		if (bl->bgid == bgid || bgid == -1U)
+	list_for_each_entry(bl, hash_list, list) {
+		if (bl->bgid == bgid || bgid == -1U) {
+			ctx->io_bl_bgid = bgid;
+			ctx->io_bl_last = bl;
 			return bl;
+		}
+	}
 
 	return NULL;
 }
@@ -1760,6 +1769,7 @@ static __cold struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
 		goto err;
 	for (i = 0; i < (1U << IO_BUFFERS_HASH_BITS); i++)
 		INIT_LIST_HEAD(&ctx->io_buffers[i]);
+	ctx->io_bl_bgid = -1U;
 
 	if (percpu_ref_init(&ctx->refs, io_ring_ctx_ref_free,
 			    PERCPU_REF_ALLOW_REINIT, GFP_KERNEL))
-- 
2.35.1