io_uring: optimise io_req_local_work_add

Chains of memory accesses are never good for performance.
The req->task->io_uring->in_cancel in io_req_local_work_add() is there
so that when a task is exiting via io_uring_try_cancel_requests() and
starts waiting for completions, it gets woken up by every new task_work
item queued.

Do a little trick by announcing waiting in io_uring_try_cancel_requests(),
making io_req_local_work_add() wake us up. We also need to check for
deferred tw items after prepare_to_wait(TASK_INTERRUPTIBLE);

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/fb11597e9bbcb365901824f8c5c2cf0d6ee100d0.1680782017.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 0ea50c4..9bbf582 100644 (file)
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -1335,10 +1335,6 @@ static void io_req_local_work_add(struct io_kiocb *req, unsigned flags)
                              &req->io_task_work.node));
 
        if (!first) {
-               if (unlikely(atomic_read(&req->task->io_uring->in_cancel))) {
-                       io_move_task_work_from_local(ctx);
-                       return;
-               }
                if (ctx->flags & IORING_SETUP_TASKRUN_FLAG)
                        atomic_or(IORING_SQ_TASKRUN, &ctx->rings->sq_flags);
                if (ctx->has_evfd)
@@ -3205,6 +3201,12 @@ static __cold bool io_uring_try_cancel_requests(struct io_ring_ctx *ctx,
        enum io_wq_cancel cret;
        bool ret = false;
 
+       /* set it so io_req_local_work_add() would wake us up */
+       if (ctx->flags & IORING_SETUP_DEFER_TASKRUN) {
+               atomic_set(&ctx->cq_wait_nr, 1);
+               smp_mb();
+       }
+
        /* failed during ring init, it couldn't have issued any requests */
        if (!ctx->rings)
                return false;
@@ -3259,6 +3261,8 @@ __cold void io_uring_cancel_generic(bool cancel_all, struct io_sq_data *sqd)
 {
        struct io_uring_task *tctx = current->io_uring;
        struct io_ring_ctx *ctx;
+       struct io_tctx_node *node;
+       unsigned long index;
        s64 inflight;
        DEFINE_WAIT(wait);
 
@@ -3280,9 +3284,6 @@ __cold void io_uring_cancel_generic(bool cancel_all, struct io_sq_data *sqd)
                        break;
 
                if (!sqd) {
-                       struct io_tctx_node *node;
-                       unsigned long index;
-
                        xa_for_each(&tctx->xa, index, node) {
                                /* sqpoll task will cancel all its requests */
                                if (node->ctx->sq_data)
@@ -3305,7 +3306,13 @@ __cold void io_uring_cancel_generic(bool cancel_all, struct io_sq_data *sqd)
                prepare_to_wait(&tctx->wait, &wait, TASK_INTERRUPTIBLE);
                io_run_task_work();
                io_uring_drop_tctx_refs(current);
-
+               xa_for_each(&tctx->xa, index, node) {
+                       if (!llist_empty(&node->ctx->work_llist)) {
+                               WARN_ON_ONCE(node->ctx->submitter_task &&
+                                            node->ctx->submitter_task != current);
+                               goto end_wait;
+                       }
+               }
                /*
                 * If we've seen completions, retry without waiting. This
                 * avoids a race where a completion comes in before we did
@@ -3313,6 +3320,7 @@ __cold void io_uring_cancel_generic(bool cancel_all, struct io_sq_data *sqd)
                 */
                if (inflight == tctx_inflight(tctx, !cancel_all))
                        schedule();
+end_wait:
                finish_wait(&tctx->wait, &wait);
        } while (1);