io_uring: optimise task_work submit flushing

tctx_task_work() tries to fetch a next batch of requests, but before it
would flush completions from the previous batch that may be sub-optimal.
E.g. io_req_task_queue() executes a head of the link where all the
linked may be enqueued through the same io_req_task_queue(). And there
are more cases for that.

Do the flushing at the end, so it can cache completions of several waves
of a single tctx_task_work(), and do the flush at the very end.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/3cac83934e4fbce520ff8025c3524398b3ae0270.1623949695.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 dc71850..49f0648 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1890,13 +1890,13 @@ static void ctx_flush_and_put(struct io_ring_ctx *ctx)
 
 static void tctx_task_work(struct callback_head *cb)
 {
+       struct io_ring_ctx *ctx = NULL;
        struct io_uring_task *tctx = container_of(cb, struct io_uring_task,
                                                  task_work);
 
        clear_bit(0, &tctx->task_state);
 
        while (!wq_list_empty(&tctx->task_list)) {
-               struct io_ring_ctx *ctx = NULL;
                struct io_wq_work_list list;
                struct io_wq_work_node *node;
 
@@ -1920,11 +1920,12 @@ static void tctx_task_work(struct callback_head *cb)
                        node = next;
                }
 
-               ctx_flush_and_put(ctx);
                if (!list.first)
                        break;
                cond_resched();
        }
+
+       ctx_flush_and_put(ctx);
 }
 
 static int io_req_task_work_add(struct io_kiocb *req)