io_uring: complete notifiers in tw

We need a task context to post CQEs but using wq is too expensive.
Try to complete notifiers using task_work and fall back to wq if fails.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/089799ab665b10b78fdc614ae6d59fa7ef0d5f91.1657643355.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/io_uring/notif.c b/io_uring/notif.c
index b257db2..aec74f8 100644 (file)
--- a/io_uring/notif.c
+++ b/io_uring/notif.c
@@ -13,6 +13,11 @@ static void __io_notif_complete_tw(struct callback_head *cb)
        struct io_notif *notif = container_of(cb, struct io_notif, task_work);
        struct io_ring_ctx *ctx = notif->ctx;
 
+       if (likely(notif->task)) {
+               io_put_task(notif->task, 1);
+               notif->task = NULL;
+       }
+
        io_cq_lock(ctx);
        io_fill_cqe_aux(ctx, notif->tag, 0, notif->seq, true);
 
@@ -43,6 +48,14 @@ static void io_uring_tx_zerocopy_callback(struct sk_buff *skb,
 
        if (!refcount_dec_and_test(&uarg->refcnt))
                return;
+
+       if (likely(notif->task)) {
+               init_task_work(&notif->task_work, __io_notif_complete_tw);
+               if (likely(!task_work_add(notif->task, &notif->task_work,
+                                         TWA_SIGNAL)))
+                       return;
+       }
+
        INIT_WORK(&notif->commit_work, io_notif_complete_wq);
        queue_work(system_unbound_wq, &notif->commit_work);
 }
@@ -134,12 +147,15 @@ __cold int io_notif_unregister(struct io_ring_ctx *ctx)
        for (i = 0; i < ctx->nr_notif_slots; i++) {
                struct io_notif_slot *slot = &ctx->notif_slots[i];
 
-               if (slot->notif)
-                       io_notif_slot_flush(slot);
+               if (!slot->notif)
+                       continue;
+               if (WARN_ON_ONCE(slot->notif->task))
+                       slot->notif->task = NULL;
+               io_notif_slot_flush(slot);
        }
 
        kvfree(ctx->notif_slots);
        ctx->notif_slots = NULL;
        ctx->nr_notif_slots = 0;
        return 0;
-}
\ No newline at end of file
+}

diff --git a/io_uring/notif.h b/io_uring/notif.h
index b23c9c0..23ca762 100644 (file)
--- a/io_uring/notif.h
+++ b/io_uring/notif.h
@@ -11,6 +11,9 @@ struct io_notif {
        struct ubuf_info        uarg;
        struct io_ring_ctx      *ctx;
 
+       /* complete via tw if ->task is non-NULL, fallback to wq otherwise */
+       struct task_struct      *task;
+
        /* cqe->user_data, io_notif_slot::tag if not overridden */
        u64                     tag;
        /* see struct io_notif_slot::seq */