io_uring/sqpoll: manage task_work privately

Decouple from task_work running, and cap the number of entries we process
at the time. If we exceed that number, push remaining entries to a retry
list that we'll process first next time.

We cap the number of entries to process at 8, which is fairly random.
We just want to get enough per-ctx batching here, while not processing
endlessly.

Since we manually run PF_IO_WORKER related task_work anyway as the task
never exits to userspace, with this we no longer need to add an actual
task_work item to the per-process list.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 18 insertions, 6 deletions

diff --git a/io_uring/io_uring.h b/io_uring/io_uring.h
index 46795ee462df..38af82788786 100644
--- a/io_uring/io_uring.h
+++ b/io_uring/io_uring.h
@@ -57,6 +57,8 @@ void io_queue_iowq(struct io_kiocb *req, struct io_tw_state *ts_dont_use);
 void io_req_task_complete(struct io_kiocb *req, struct io_tw_state *ts);
 void io_req_task_queue_fail(struct io_kiocb *req, int ret);
 void io_req_task_submit(struct io_kiocb *req, struct io_tw_state *ts);
+struct llist_node *io_handle_tw_list(struct llist_node *node, unsigned int *count, unsigned int max_entries);
+struct llist_node *tctx_task_work_run(struct io_uring_task *tctx, unsigned int max_entries, unsigned int *count);
 void tctx_task_work(struct callback_head *cb);
 __cold void io_uring_cancel_generic(bool cancel_all, struct io_sq_data *sqd);
 int io_uring_alloc_task_context(struct task_struct *task,
@@ -275,6 +277,8 @@ static inline unsigned int io_sqring_entries(struct io_ring_ctx *ctx)
 
 static inline int io_run_task_work(void)
 {
+	bool ret = false;
+
 	/*
 	 * Always check-and-clear the task_work notification signal. With how
 	 * signaling works for task_work, we can find it set with nothing to
@@ -286,18 +290,26 @@ static inline int io_run_task_work(void)
 	 * PF_IO_WORKER never returns to userspace, so check here if we have
 	 * notify work that needs processing.
 	 */
-	if (current->flags & PF_IO_WORKER &&
-	    test_thread_flag(TIF_NOTIFY_RESUME)) {
-		__set_current_state(TASK_RUNNING);
-		resume_user_mode_work(NULL);
+	if (current->flags & PF_IO_WORKER) {
+		if (test_thread_flag(TIF_NOTIFY_RESUME)) {
+			__set_current_state(TASK_RUNNING);
+			resume_user_mode_work(NULL);
+		}
+		if (current->io_uring) {
+			unsigned int count = 0;
+
+			tctx_task_work_run(current->io_uring, UINT_MAX, &count);
+			if (count)
+				ret = true;
+		}
 	}
 	if (task_work_pending(current)) {
 		__set_current_state(TASK_RUNNING);
 		task_work_run();
-		return 1;
+		ret = true;
 	}
 
-	return 0;
+	return ret;
 }
 
 static inline bool io_task_work_pending(struct io_ring_ctx *ctx)