public inbox for [email protected]
 help / color / mirror / Atom feed
From: Dylan Yudaken <[email protected]>
To: Jens Axboe <[email protected]>,
	Pavel Begunkov <[email protected]>,
	<[email protected]>
Cc: <[email protected]>, Dylan Yudaken <[email protected]>
Subject: [PATCH for-next v2 6/6] io_uring: signal registered eventfd to process deferred task work
Date: Tue, 16 Aug 2022 08:37:28 -0700	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>

Some workloads rely on a registered eventfd (via
io_uring_register_eventfd(3)) in order to wake up and process the
io_uring.

In the case of a ring setup with IORING_SETUP_DEFER_TASKRUN, that eventfd
also needs to be signalled when there are tasks to run.

This changes an old behaviour which assumed 1 eventfd signal implied at
least 1 CQE, however only when this new flag is set (and so old users will
not notice). This should be expected with the IORING_SETUP_DEFER_TASKRUN
flag as it is not guaranteed that every task will result in a CQE.

Signed-off-by: Dylan Yudaken <[email protected]>
---
 include/linux/io_uring_types.h |  1 +
 io_uring/io_uring.c            | 75 ++++++++++++++++++++++++----------
 2 files changed, 55 insertions(+), 21 deletions(-)

diff --git a/include/linux/io_uring_types.h b/include/linux/io_uring_types.h
index d56ff2185168..42494176434a 100644
--- a/include/linux/io_uring_types.h
+++ b/include/linux/io_uring_types.h
@@ -184,6 +184,7 @@ struct io_ev_fd {
 	struct eventfd_ctx	*cq_ev_fd;
 	unsigned int		eventfd_async: 1;
 	struct rcu_head		rcu;
+	atomic_t		refs;
 };
 
 struct io_alloc_cache {
diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 2eb9ad9edef3..65ea8ccd63e8 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -478,33 +478,33 @@ static __cold void io_queue_deferred(struct io_ring_ctx *ctx)
 	}
 }
 
+
+static inline void __io_eventfd_put(struct io_ev_fd *ev_fd)
+{
+	if (atomic_dec_and_test(&ev_fd->refs)) {
+		eventfd_ctx_put(ev_fd->cq_ev_fd);
+		kfree(ev_fd);
+	}
+}
+
+static void io_eventfd_signal_put(struct rcu_head *rcu)
+{
+	struct io_ev_fd *ev_fd = container_of(rcu, struct io_ev_fd, rcu);
+
+	eventfd_signal(ev_fd->cq_ev_fd, 1);
+	__io_eventfd_put(ev_fd);
+}
+
 static void io_eventfd_put(struct rcu_head *rcu)
 {
 	struct io_ev_fd *ev_fd = container_of(rcu, struct io_ev_fd, rcu);
 
-	eventfd_ctx_put(ev_fd->cq_ev_fd);
-	kfree(ev_fd);
+	__io_eventfd_put(ev_fd);
 }
 
 static void io_eventfd_signal(struct io_ring_ctx *ctx)
 {
-	struct io_ev_fd *ev_fd;
-	bool skip;
-
-	spin_lock(&ctx->completion_lock);
-	/*
-	 * Eventfd should only get triggered when at least one event has been
-	 * posted. Some applications rely on the eventfd notification count only
-	 * changing IFF a new CQE has been added to the CQ ring. There's no
-	 * depedency on 1:1 relationship between how many times this function is
-	 * called (and hence the eventfd count) and number of CQEs posted to the
-	 * CQ ring.
-	 */
-	skip = ctx->cached_cq_tail == ctx->evfd_last_cq_tail;
-	ctx->evfd_last_cq_tail = ctx->cached_cq_tail;
-	spin_unlock(&ctx->completion_lock);
-	if (skip)
-		return;
+	struct io_ev_fd *ev_fd = NULL;
 
 	rcu_read_lock();
 	/*
@@ -522,13 +522,43 @@ static void io_eventfd_signal(struct io_ring_ctx *ctx)
 		goto out;
 	if (READ_ONCE(ctx->rings->cq_flags) & IORING_CQ_EVENTFD_DISABLED)
 		goto out;
+	if (ev_fd->eventfd_async && !io_wq_current_is_worker())
+		goto out;
 
-	if (!ev_fd->eventfd_async || io_wq_current_is_worker())
+	if (likely(eventfd_signal_allowed())) {
 		eventfd_signal(ev_fd->cq_ev_fd, 1);
+	} else {
+		atomic_inc(&ev_fd->refs);
+		call_rcu(&ev_fd->rcu, io_eventfd_signal_put);
+	}
+
 out:
 	rcu_read_unlock();
 }
 
+static void io_eventfd_flush_signal(struct io_ring_ctx *ctx)
+{
+	bool skip;
+
+	spin_lock(&ctx->completion_lock);
+
+	/*
+	 * Eventfd should only get triggered when at least one event has been
+	 * posted. Some applications rely on the eventfd notification count
+	 * only changing IFF a new CQE has been added to the CQ ring. There's
+	 * no depedency on 1:1 relationship between how many times this
+	 * function is called (and hence the eventfd count) and number of CQEs
+	 * posted to the CQ ring.
+	 */
+	skip = ctx->cached_cq_tail == ctx->evfd_last_cq_tail;
+	ctx->evfd_last_cq_tail = ctx->cached_cq_tail;
+	spin_unlock(&ctx->completion_lock);
+	if (skip)
+		return;
+
+	io_eventfd_signal(ctx);
+}
+
 void __io_commit_cqring_flush(struct io_ring_ctx *ctx)
 {
 	if (ctx->off_timeout_used || ctx->drain_active) {
@@ -540,7 +570,7 @@ void __io_commit_cqring_flush(struct io_ring_ctx *ctx)
 		spin_unlock(&ctx->completion_lock);
 	}
 	if (ctx->has_evfd)
-		io_eventfd_signal(ctx);
+		io_eventfd_flush_signal(ctx);
 }
 
 static inline void io_cqring_ev_posted(struct io_ring_ctx *ctx)
@@ -1066,6 +1096,8 @@ static void io_req_local_work_add(struct io_kiocb *req)
 	if (ctx->flags & IORING_SETUP_TASKRUN_FLAG)
 		atomic_or(IORING_SQ_TASKRUN, &ctx->rings->sq_flags);
 
+	if (ctx->has_evfd)
+		io_eventfd_signal(ctx);
 	io_cqring_wake(ctx);
 }
 
@@ -2443,6 +2475,7 @@ static int io_eventfd_register(struct io_ring_ctx *ctx, void __user *arg,
 	ev_fd->eventfd_async = eventfd_async;
 	ctx->has_evfd = true;
 	rcu_assign_pointer(ctx->io_ev_fd, ev_fd);
+	atomic_set(&ev_fd->refs, 1);
 	return 0;
 }
 
-- 
2.30.2


      parent reply	other threads:[~2022-08-16 15:39 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-08-16 15:37 [PATCH for-next v2 0/6] io_uring: defer task work to when it is needed Dylan Yudaken
2022-08-16 15:37 ` [PATCH for-next v2 1/6] io_uring: remove unnecessary variable Dylan Yudaken
2022-08-16 15:37 ` [PATCH for-next v2 2/6] io_uring: introduce io_has_work Dylan Yudaken
2022-08-16 15:37 ` [PATCH for-next v2 3/6] io_uring: do not run task work at the start of io_uring_enter Dylan Yudaken
2022-08-16 15:37 ` [PATCH for-next v2 4/6] io_uring: add IORING_SETUP_DEFER_TASKRUN Dylan Yudaken
2022-08-18 10:42   ` Pavel Begunkov
2022-08-18 14:18     ` Dylan Yudaken
2022-08-16 15:37 ` [PATCH for-next v2 5/6] io_uring: move io_eventfd_put Dylan Yudaken
2022-08-16 15:37 ` Dylan Yudaken [this message]

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    [email protected] \
    [email protected] \
    [email protected] \
    [email protected] \
    [email protected] \
    [email protected] \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox