io_uring: switch !DRAIN fast path when possible

->drain_used is one way, which is not optimal if users use DRAIN but
very rarely. However, we can just clear it in io_drain_req() when all
drained before requests are gone. Also rename the flag to reflect the
change and be more clear about it.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/7f37a240857546a94df6348507edddacab150460.1623772051.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 6292b8d..25106cf 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -352,7 +352,7 @@ struct io_ring_ctx {
                unsigned int            eventfd_async: 1;
                unsigned int            restricted: 1;
                unsigned int            off_timeout_used: 1;
-               unsigned int            drain_used: 1;
+               unsigned int            drain_active: 1;
        } ____cacheline_aligned_in_smp;
 
        /* submission data */
@@ -1346,10 +1346,10 @@ static void io_flush_timeouts(struct io_ring_ctx *ctx)
 
 static void io_commit_cqring(struct io_ring_ctx *ctx)
 {
-       if (unlikely(ctx->off_timeout_used || ctx->drain_used)) {
+       if (unlikely(ctx->off_timeout_used || ctx->drain_active)) {
                if (ctx->off_timeout_used)
                        io_flush_timeouts(ctx);
-               if (ctx->drain_used)
+               if (ctx->drain_active)
                        io_queue_deferred(ctx);
        }
        /* order cqe stores with ring update */
@@ -6004,8 +6004,10 @@ static bool io_drain_req(struct io_kiocb *req)
 
        /* Still need defer if there is pending req in defer list. */
        if (likely(list_empty_careful(&ctx->defer_list) &&
-               !(req->flags & REQ_F_IO_DRAIN)))
+               !(req->flags & REQ_F_IO_DRAIN))) {
+               ctx->drain_active = false;
                return false;
+       }
 
        seq = io_get_sequence(req);
        /* Still a chance to pass the sequence check */
@@ -6446,7 +6448,7 @@ static void __io_queue_sqe(struct io_kiocb *req)
 
 static inline void io_queue_sqe(struct io_kiocb *req)
 {
-       if (unlikely(req->ctx->drain_used) && io_drain_req(req))
+       if (unlikely(req->ctx->drain_active) && io_drain_req(req))
                return;
 
        if (likely(!(req->flags & REQ_F_FORCE_ASYNC))) {
@@ -6572,7 +6574,7 @@ fail_req:
        }
 
        if (unlikely(req->flags & REQ_F_IO_DRAIN)) {
-               ctx->drain_used = true;
+               ctx->drain_active = true;
 
                /*
                 * Taking sequential execution of a link, draining both sides