[PATCH v4 0/6] napi tracking strategy

[PATCH v4 0/6] napi tracking strategy

[Olivier Langlois]

the actual napi tracking strategy is inducing a non-negligeable overhead.
Everytime a multishot poll is triggered or any poll armed, if the napi is
enabled on the ring a lookup is performed to either add a new napi id into
the napi_list or its timeout value is updated.

For many scenarios, this is overkill as the napi id list will be pretty
much static most of the time. To address this common scenario, the concept of io_uring_napi_tracking_strategy has been created.
the tracking strategy can be specified when io_register_napi() is called.

To keep backward compatibility, the legacy strategy IO_URING_NAPI_TRACKING_DYNAMIC is assigned the value 0 so that existing code using io_uring napi busy polling continue working as before. If IO_URING_NAPI_TRACKING_STATIC is provided, io_napi_add() becomes a noop function and the responsability to update the napi devices list is given to the user by calling io_register_napi() with the opcode value of IO_URING_NAPI_STATIC_ADD_ID or IO_URING_NAPI_STATIC_DEL_ID.

the NAPI ids used by a process can be discovered by calling
getsockopt(fd, SOL_SOCKET, SO_INCOMING_NAPI_ID, &napi_id, &len)

the patch serie consist of very minor fixes followed by the core of the changes
to implement the new feature.

v4 changes:
- improve cover letter text
- rebase patch on for-6.13/io_uring
- create a prep-patch for the __io_napi_add refactoring change
- create a prep-patch for the Scope-Based Resource Management refactoring
- create a prep-patch for the __io_napi_do_busy_loop cleanup
- adress io_napi_add() code review comment

v3 changes:
- address minor comments in patch #3
- replace the double for loop hash macro with the single loop list macro to iterate the napi elements in patch #2
- add __cold attribute to common_tracking_show_fdinfo() and napi_show_fdinfo()

v2 changes:
- extract small changes from the core changes to ease minor fixes backport
- totally remove the io_napi_tracking_ops interface

Olivier Langlois (6):
  io_uring/napi: protect concurrent io_napi_entry timeout accesses
  io_uring/napi: fix io_napi_entry RCU accesses
  io_uring/napi: improve __io_napi_add
  io_uring/napi: Use lock guards
  io_uring/napi: clean up __io_napi_do_busy_loop
  io_uring/napi: add static napi tracking strategy

 include/linux/io_uring_types.h |   2 +-
 include/uapi/linux/io_uring.h  |  32 +++++-
 io_uring/fdinfo.c              |  54 +++++++---
 io_uring/napi.c                | 184 +++++++++++++++++++++++----------
 io_uring/napi.h                |   8 +-
 5 files changed, 207 insertions(+), 73 deletions(-)

-- 
2.47.0

[PATCH v4 1/6] io_uring/napi: protect concurrent io_napi_entry timeout accesses

[Olivier Langlois]

io_napi_entry timeout value can be updated while accessed from the poll
functions.

Its concurrent accesses are wrapped with READ_ONCE()/WRITE_ONCE() macros
to avoid incorrect compiler optimizations.

Signed-off-by: Olivier Langlois <olivier@trillion01.com>
---
 io_uring/napi.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/io_uring/napi.c b/io_uring/napi.c
index d0cf694d0172..dda2e083fb5d 100644
--- a/io_uring/napi.c
+++ b/io_uring/napi.c
@@ -60,7 +60,7 @@ void __io_napi_add(struct io_ring_ctx *ctx, struct socket *sock)
 	rcu_read_lock();
 	e = io_napi_hash_find(hash_list, napi_id);
 	if (e) {
-		e->timeout = jiffies + NAPI_TIMEOUT;
+		WRITE_ONCE(e->timeout, jiffies + NAPI_TIMEOUT);
 		rcu_read_unlock();
 		return;
 	}
@@ -92,7 +92,7 @@ static void __io_napi_remove_stale(struct io_ring_ctx *ctx)
 
 	spin_lock(&ctx->napi_lock);
 	hash_for_each(ctx->napi_ht, i, e, node) {
-		if (time_after(jiffies, e->timeout)) {
+		if (time_after(jiffies, READ_ONCE(e->timeout))) {
 			list_del(&e->list);
 			hash_del_rcu(&e->node);
 			kfree_rcu(e, rcu);
@@ -150,7 +150,7 @@ static bool __io_napi_do_busy_loop(struct io_ring_ctx *ctx,
 		napi_busy_loop_rcu(e->napi_id, loop_end, loop_end_arg,
 				   ctx->napi_prefer_busy_poll, BUSY_POLL_BUDGET);
 
-		if (time_after(jiffies, e->timeout))
+		if (time_after(jiffies, READ_ONCE(e->timeout)))
 			is_stale = true;
 	}
 
-- 
2.47.0

[PATCH v4 2/6] io_uring/napi: fix io_napi_entry RCU accesses

[Olivier Langlois]

correct 3 RCU structures modifications that were not using the RCU
functions to make their update.

Signed-off-by: Olivier Langlois <olivier@trillion01.com>
---
 io_uring/napi.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/io_uring/napi.c b/io_uring/napi.c
index dda2e083fb5d..921de9de8d75 100644
--- a/io_uring/napi.c
+++ b/io_uring/napi.c
@@ -81,19 +81,24 @@ void __io_napi_add(struct io_ring_ctx *ctx, struct socket *sock)
 	}
 
 	hlist_add_tail_rcu(&e->node, hash_list);
-	list_add_tail(&e->list, &ctx->napi_list);
+	list_add_tail_rcu(&e->list, &ctx->napi_list);
 	spin_unlock(&ctx->napi_lock);
 }
 
 static void __io_napi_remove_stale(struct io_ring_ctx *ctx)
 {
 	struct io_napi_entry *e;
-	unsigned int i;
 
 	spin_lock(&ctx->napi_lock);
-	hash_for_each(ctx->napi_ht, i, e, node) {
+	/*
+	 * list_for_each_entry_safe() is not required as long as:
+	 * 1. list_del_rcu() does not reset the deleted node next pointer
+	 * 2. kfree_rcu() delays the memory freeing until the next quiescent
+	 *    state
+	 */
+	list_for_each_entry(e, &ctx->napi_list, list) {
 		if (time_after(jiffies, READ_ONCE(e->timeout))) {
-			list_del(&e->list);
+			list_del_rcu(&e->list);
 			hash_del_rcu(&e->node);
 			kfree_rcu(e, rcu);
 		}
@@ -204,13 +209,13 @@ void io_napi_init(struct io_ring_ctx *ctx)
 void io_napi_free(struct io_ring_ctx *ctx)
 {
 	struct io_napi_entry *e;
-	unsigned int i;
 
 	spin_lock(&ctx->napi_lock);
-	hash_for_each(ctx->napi_ht, i, e, node) {
+	list_for_each_entry(e, &ctx->napi_list, list) {
 		hash_del_rcu(&e->node);
 		kfree_rcu(e, rcu);
 	}
+	INIT_LIST_HEAD_RCU(&ctx->napi_list);
 	spin_unlock(&ctx->napi_lock);
 }
 
-- 
2.47.0

[PATCH v4 3/6] io_uring/napi: improve __io_napi_add

[Olivier Langlois]

1. move the sock->sk pointer validity test outside the function to
   avoid the function call overhead and to make the function more
   more reusable
2. change its name to __io_napi_add_id to be more precise about it is
   doing
3. return an error code to report errors

Signed-off-by: Olivier Langlois <olivier@trillion01.com>
---
 io_uring/napi.c | 19 ++++++-------------
 io_uring/napi.h |  6 +++---
 2 files changed, 9 insertions(+), 16 deletions(-)

diff --git a/io_uring/napi.c b/io_uring/napi.c
index 921de9de8d75..5e2299e7ff8e 100644
--- a/io_uring/napi.c
+++ b/io_uring/napi.c
@@ -38,22 +38,14 @@ static inline ktime_t net_to_ktime(unsigned long t)
 	return ns_to_ktime(t << 10);
 }
 
-void __io_napi_add(struct io_ring_ctx *ctx, struct socket *sock)
+int __io_napi_add_id(struct io_ring_ctx *ctx, unsigned int napi_id)
 {
 	struct hlist_head *hash_list;
-	unsigned int napi_id;
-	struct sock *sk;
 	struct io_napi_entry *e;
 
-	sk = sock->sk;
-	if (!sk)
-		return;
-
-	napi_id = READ_ONCE(sk->sk_napi_id);
-
 	/* Non-NAPI IDs can be rejected. */
 	if (napi_id < MIN_NAPI_ID)
-		return;
+		return -EINVAL;
 
 	hash_list = &ctx->napi_ht[hash_min(napi_id, HASH_BITS(ctx->napi_ht))];
 
@@ -62,13 +54,13 @@ void __io_napi_add(struct io_ring_ctx *ctx, struct socket *sock)
 	if (e) {
 		WRITE_ONCE(e->timeout, jiffies + NAPI_TIMEOUT);
 		rcu_read_unlock();
-		return;
+		return -EEXIST;
 	}
 	rcu_read_unlock();
 
 	e = kmalloc(sizeof(*e), GFP_NOWAIT);
 	if (!e)
-		return;
+		return -ENOMEM;
 
 	e->napi_id = napi_id;
 	e->timeout = jiffies + NAPI_TIMEOUT;
@@ -77,12 +69,13 @@ void __io_napi_add(struct io_ring_ctx *ctx, struct socket *sock)
 	if (unlikely(io_napi_hash_find(hash_list, napi_id))) {
 		spin_unlock(&ctx->napi_lock);
 		kfree(e);
-		return;
+		return -EEXIST;
 	}
 
 	hlist_add_tail_rcu(&e->node, hash_list);
 	list_add_tail_rcu(&e->list, &ctx->napi_list);
 	spin_unlock(&ctx->napi_lock);
+	return 0;
 }
 
 static void __io_napi_remove_stale(struct io_ring_ctx *ctx)
diff --git a/io_uring/napi.h b/io_uring/napi.h
index fd275ef0456d..4ae622f37b30 100644
--- a/io_uring/napi.h
+++ b/io_uring/napi.h
@@ -15,7 +15,7 @@ void io_napi_free(struct io_ring_ctx *ctx);
 int io_register_napi(struct io_ring_ctx *ctx, void __user *arg);
 int io_unregister_napi(struct io_ring_ctx *ctx, void __user *arg);
 
-void __io_napi_add(struct io_ring_ctx *ctx, struct socket *sock);
+int __io_napi_add_id(struct io_ring_ctx *ctx, unsigned int napi_id);
 
 void __io_napi_busy_loop(struct io_ring_ctx *ctx, struct io_wait_queue *iowq);
 int io_napi_sqpoll_busy_poll(struct io_ring_ctx *ctx);
@@ -48,8 +48,8 @@ static inline void io_napi_add(struct io_kiocb *req)
 		return;
 
 	sock = sock_from_file(req->file);
-	if (sock)
-		__io_napi_add(ctx, sock);
+	if (sock && sock->sk)
+		__io_napi_add_id(ctx, READ_ONCE(sock->sk->sk_napi_id));
 }
 
 #else
-- 
2.47.0

[PATCH v4 4/6] io_uring/napi: Use lock guards

[Olivier Langlois]

Convert napi locks to use the shiny new Scope-Based Resource Management
machinery.

Signed-off-by: Olivier Langlois <olivier@trillion01.com>
---
 io_uring/napi.c | 40 +++++++++++++++++++++-------------------
 1 file changed, 21 insertions(+), 19 deletions(-)

diff --git a/io_uring/napi.c b/io_uring/napi.c
index 5e2299e7ff8e..6d5fdd397f2f 100644
--- a/io_uring/napi.c
+++ b/io_uring/napi.c
@@ -49,14 +49,13 @@ int __io_napi_add_id(struct io_ring_ctx *ctx, unsigned int napi_id)
 
 	hash_list = &ctx->napi_ht[hash_min(napi_id, HASH_BITS(ctx->napi_ht))];
 
-	rcu_read_lock();
-	e = io_napi_hash_find(hash_list, napi_id);
-	if (e) {
-		WRITE_ONCE(e->timeout, jiffies + NAPI_TIMEOUT);
-		rcu_read_unlock();
-		return -EEXIST;
+	scoped_guard(rcu) {
+		e = io_napi_hash_find(hash_list, napi_id);
+		if (e) {
+			WRITE_ONCE(e->timeout, jiffies + NAPI_TIMEOUT);
+			return -EEXIST;
+		}
 	}
-	rcu_read_unlock();
 
 	e = kmalloc(sizeof(*e), GFP_NOWAIT);
 	if (!e)
@@ -65,6 +64,10 @@ int __io_napi_add_id(struct io_ring_ctx *ctx, unsigned int napi_id)
 	e->napi_id = napi_id;
 	e->timeout = jiffies + NAPI_TIMEOUT;
 
+	/*
+	 * guard(spinlock) is not used to manually unlock it before calling
+	 * kfree()
+	 */
 	spin_lock(&ctx->napi_lock);
 	if (unlikely(io_napi_hash_find(hash_list, napi_id))) {
 		spin_unlock(&ctx->napi_lock);
@@ -82,7 +85,7 @@ static void __io_napi_remove_stale(struct io_ring_ctx *ctx)
 {
 	struct io_napi_entry *e;
 
-	spin_lock(&ctx->napi_lock);
+	guard(spinlock)(&ctx->napi_lock);
 	/*
 	 * list_for_each_entry_safe() is not required as long as:
 	 * 1. list_del_rcu() does not reset the deleted node next pointer
@@ -96,7 +99,6 @@ static void __io_napi_remove_stale(struct io_ring_ctx *ctx)
 			kfree_rcu(e, rcu);
 		}
 	}
-	spin_unlock(&ctx->napi_lock);
 }
 
 static inline void io_napi_remove_stale(struct io_ring_ctx *ctx, bool is_stale)
@@ -168,11 +170,12 @@ static void io_napi_blocking_busy_loop(struct io_ring_ctx *ctx,
 	if (list_is_singular(&ctx->napi_list))
 		loop_end_arg = iowq;
 
-	rcu_read_lock();
-	do {
-		is_stale = __io_napi_do_busy_loop(ctx, loop_end_arg);
-	} while (!io_napi_busy_loop_should_end(iowq, start_time) && !loop_end_arg);
-	rcu_read_unlock();
+	scoped_guard(rcu) {
+		do {
+			is_stale = __io_napi_do_busy_loop(ctx, loop_end_arg);
+		} while (!io_napi_busy_loop_should_end(iowq, start_time) &&
+			 !loop_end_arg);
+	}
 
 	io_napi_remove_stale(ctx, is_stale);
 }
@@ -203,13 +206,12 @@ void io_napi_free(struct io_ring_ctx *ctx)
 {
 	struct io_napi_entry *e;
 
-	spin_lock(&ctx->napi_lock);
+	guard(spinlock)(&ctx->napi_lock);
 	list_for_each_entry(e, &ctx->napi_list, list) {
 		hash_del_rcu(&e->node);
 		kfree_rcu(e, rcu);
 	}
 	INIT_LIST_HEAD_RCU(&ctx->napi_list);
-	spin_unlock(&ctx->napi_lock);
 }
 
 /*
@@ -305,9 +307,9 @@ int io_napi_sqpoll_busy_poll(struct io_ring_ctx *ctx)
 	if (list_empty_careful(&ctx->napi_list))
 		return 0;
 
-	rcu_read_lock();
-	is_stale = __io_napi_do_busy_loop(ctx, NULL);
-	rcu_read_unlock();
+	scoped_guard(rcu) {
+		is_stale = __io_napi_do_busy_loop(ctx, NULL);
+	}
 
 	io_napi_remove_stale(ctx, is_stale);
 	return 1;
-- 
2.47.0

[PATCH v4 5/6] io_uring/napi: clean up __io_napi_do_busy_loop

[Olivier Langlois]

__io_napi_do_busy_loop now requires to have loop_end in its parameters.
This makes the code cleaner and also has the benefit of removing a
branch since the only caller not passing NULL for loop_end_arg is also
setting the value conditionally.

Signed-off-by: Olivier Langlois <olivier@trillion01.com>
---
 io_uring/napi.c | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/io_uring/napi.c b/io_uring/napi.c
index 6d5fdd397f2f..1de1543d8034 100644
--- a/io_uring/napi.c
+++ b/io_uring/napi.c
@@ -137,15 +137,12 @@ static bool io_napi_busy_loop_should_end(void *data,
 }
 
 static bool __io_napi_do_busy_loop(struct io_ring_ctx *ctx,
+				   bool (*loop_end)(void *, unsigned long),
 				   void *loop_end_arg)
 {
 	struct io_napi_entry *e;
-	bool (*loop_end)(void *, unsigned long) = NULL;
 	bool is_stale = false;
 
-	if (loop_end_arg)
-		loop_end = io_napi_busy_loop_should_end;
-
 	list_for_each_entry_rcu(e, &ctx->napi_list, list) {
 		napi_busy_loop_rcu(e->napi_id, loop_end, loop_end_arg,
 				   ctx->napi_prefer_busy_poll, BUSY_POLL_BUDGET);
@@ -161,18 +158,22 @@ static void io_napi_blocking_busy_loop(struct io_ring_ctx *ctx,
 				       struct io_wait_queue *iowq)
 {
 	unsigned long start_time = busy_loop_current_time();
+	bool (*loop_end)(void *, unsigned long) = NULL;
 	void *loop_end_arg = NULL;
 	bool is_stale = false;
 
 	/* Singular lists use a different napi loop end check function and are
 	 * only executed once.
 	 */
-	if (list_is_singular(&ctx->napi_list))
+	if (list_is_singular(&ctx->napi_list)) {
+		loop_end = io_napi_busy_loop_should_end;
 		loop_end_arg = iowq;
+	}
 
 	scoped_guard(rcu) {
 		do {
-			is_stale = __io_napi_do_busy_loop(ctx, loop_end_arg);
+			is_stale = __io_napi_do_busy_loop(ctx, loop_end,
+							  loop_end_arg);
 		} while (!io_napi_busy_loop_should_end(iowq, start_time) &&
 			 !loop_end_arg);
 	}
@@ -308,7 +309,7 @@ int io_napi_sqpoll_busy_poll(struct io_ring_ctx *ctx)
 		return 0;
 
 	scoped_guard(rcu) {
-		is_stale = __io_napi_do_busy_loop(ctx, NULL);
+		is_stale = __io_napi_do_busy_loop(ctx, NULL, NULL);
 	}
 
 	io_napi_remove_stale(ctx, is_stale);
-- 
2.47.0

[PATCH v4 6/6] io_uring/napi: add static napi tracking strategy

[Olivier Langlois]

Add the static napi tracking strategy. That allows the user to manually
manage the napi ids list for busy polling, and eliminate the overhead of
dynamically updating the list from the fast path.

Signed-off-by: Olivier Langlois <olivier@trillion01.com>
---
 include/linux/io_uring_types.h |  2 +-
 include/uapi/linux/io_uring.h  | 32 ++++++++++-
 io_uring/fdinfo.c              | 54 ++++++++++++++-----
 io_uring/napi.c                | 97 ++++++++++++++++++++++++++++++----
 io_uring/napi.h                |  2 +-
 5 files changed, 160 insertions(+), 27 deletions(-)

diff --git a/include/linux/io_uring_types.h b/include/linux/io_uring_types.h
index 4b9ba523978d..f435433f29a3 100644
--- a/include/linux/io_uring_types.h
+++ b/include/linux/io_uring_types.h
@@ -409,7 +409,7 @@ struct io_ring_ctx {
 	/* napi busy poll default timeout */
 	ktime_t			napi_busy_poll_dt;
 	bool			napi_prefer_busy_poll;
-	bool			napi_enabled;
+	u8			napi_track_mode;
 
 	DECLARE_HASHTABLE(napi_ht, 4);
 #endif
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 86cb385fe0b5..99a7a082421e 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -771,12 +771,40 @@ struct io_uring_buf_status {
 	__u32	resv[8];
 };
 
+enum io_uring_napi_op {
+	/* register/ungister backward compatible opcode */
+	IO_URING_NAPI_REGISTER_OP = 0,
+
+	/* opcodes to update napi_list when static tracking is used */
+	IO_URING_NAPI_STATIC_ADD_ID = 1,
+	IO_URING_NAPI_STATIC_DEL_ID = 2
+};
+
+enum io_uring_napi_tracking_strategy {
+	/* value must be 0 for backward compatibility */
+	IO_URING_NAPI_TRACKING_DYNAMIC = 0,
+	IO_URING_NAPI_TRACKING_STATIC = 1,
+	IO_URING_NAPI_TRACKING_INACTIVE = 255
+};
+
 /* argument for IORING_(UN)REGISTER_NAPI */
 struct io_uring_napi {
 	__u32	busy_poll_to;
 	__u8	prefer_busy_poll;
-	__u8	pad[3];
-	__u64	resv;
+
+	/* a io_uring_napi_op value */
+	__u8	opcode;
+	__u8	pad[2];
+
+	/*
+	 * for IO_URING_NAPI_REGISTER_OP, it is a
+	 * io_uring_napi_tracking_strategy value.
+	 *
+	 * for IO_URING_NAPI_STATIC_ADD_ID/IO_URING_NAPI_STATIC_DEL_ID
+	 * it is the napi id to add/del from napi_list.
+	 */
+	__u32	op_param;
+	__u32	resv;
 };
 
 /*
diff --git a/io_uring/fdinfo.c b/io_uring/fdinfo.c
index 6b1247664b35..f58d568060cb 100644
--- a/io_uring/fdinfo.c
+++ b/io_uring/fdinfo.c
@@ -46,6 +46,46 @@ static __cold int io_uring_show_cred(struct seq_file *m, unsigned int id,
 	return 0;
 }
 
+#ifdef CONFIG_NET_RX_BUSY_POLL
+static __cold void common_tracking_show_fdinfo(struct io_ring_ctx *ctx,
+					       struct seq_file *m,
+					       const char *tracking_strategy)
+{
+	seq_puts(m, "NAPI:\tenabled\n");
+	seq_printf(m, "napi tracking:\t%s\n", tracking_strategy);
+	seq_printf(m, "napi_busy_poll_dt:\t%llu\n", ctx->napi_busy_poll_dt);
+	if (ctx->napi_prefer_busy_poll)
+		seq_puts(m, "napi_prefer_busy_poll:\ttrue\n");
+	else
+		seq_puts(m, "napi_prefer_busy_poll:\tfalse\n");
+}
+
+static __cold void napi_show_fdinfo(struct io_ring_ctx *ctx,
+				    struct seq_file *m)
+{
+	unsigned int mode = READ_ONCE(ctx->napi_track_mode);
+
+	switch (mode) {
+	case IO_URING_NAPI_TRACKING_INACTIVE:
+		seq_puts(m, "NAPI:\tdisabled\n");
+		break;
+	case IO_URING_NAPI_TRACKING_DYNAMIC:
+		common_tracking_show_fdinfo(ctx, m, "dynamic");
+		break;
+	case IO_URING_NAPI_TRACKING_STATIC:
+		common_tracking_show_fdinfo(ctx, m, "static");
+		break;
+	default:
+		seq_printf(m, "NAPI:\tunknown mode (%u)\n", mode);
+	}
+}
+#else
+static inline void napi_show_fdinfo(struct io_ring_ctx *ctx,
+				    struct seq_file *m)
+{
+}
+#endif
+
 /*
  * Caller holds a reference to the file already, we don't need to do
  * anything else to get an extra reference.
@@ -221,18 +261,6 @@ __cold void io_uring_show_fdinfo(struct seq_file *m, struct file *file)
 
 	}
 	spin_unlock(&ctx->completion_lock);
-
-#ifdef CONFIG_NET_RX_BUSY_POLL
-	if (ctx->napi_enabled) {
-		seq_puts(m, "NAPI:\tenabled\n");
-		seq_printf(m, "napi_busy_poll_dt:\t%llu\n", ctx->napi_busy_poll_dt);
-		if (ctx->napi_prefer_busy_poll)
-			seq_puts(m, "napi_prefer_busy_poll:\ttrue\n");
-		else
-			seq_puts(m, "napi_prefer_busy_poll:\tfalse\n");
-	} else {
-		seq_puts(m, "NAPI:\tdisabled\n");
-	}
-#endif
+	napi_show_fdinfo(ctx, m);
 }
 #endif
diff --git a/io_uring/napi.c b/io_uring/napi.c
index 1de1543d8034..b1ade3fda30f 100644
--- a/io_uring/napi.c
+++ b/io_uring/napi.c
@@ -81,6 +81,27 @@ int __io_napi_add_id(struct io_ring_ctx *ctx, unsigned int napi_id)
 	return 0;
 }
 
+static int __io_napi_del_id(struct io_ring_ctx *ctx, unsigned int napi_id)
+{
+	struct hlist_head *hash_list;
+	struct io_napi_entry *e;
+
+	/* Non-NAPI IDs can be rejected. */
+	if (napi_id < MIN_NAPI_ID)
+		return -EINVAL;
+
+	hash_list = &ctx->napi_ht[hash_min(napi_id, HASH_BITS(ctx->napi_ht))];
+	guard(spinlock)(&ctx->napi_lock);
+	e = io_napi_hash_find(hash_list, napi_id);
+	if (!e)
+		return -ENOENT;
+
+	list_del_rcu(&e->list);
+	hash_del_rcu(&e->node);
+	kfree_rcu(e, rcu);
+	return 0;
+}
+
 static void __io_napi_remove_stale(struct io_ring_ctx *ctx)
 {
 	struct io_napi_entry *e;
@@ -136,9 +157,25 @@ static bool io_napi_busy_loop_should_end(void *data,
 	return false;
 }
 
-static bool __io_napi_do_busy_loop(struct io_ring_ctx *ctx,
-				   bool (*loop_end)(void *, unsigned long),
-				   void *loop_end_arg)
+/*
+ * never report stale entries
+ */
+static bool static_tracking_do_busy_loop(struct io_ring_ctx *ctx,
+					 bool (*loop_end)(void *, unsigned long),
+					 void *loop_end_arg)
+{
+	struct io_napi_entry *e;
+
+	list_for_each_entry_rcu(e, &ctx->napi_list, list)
+		napi_busy_loop_rcu(e->napi_id, loop_end, loop_end_arg,
+				   ctx->napi_prefer_busy_poll, BUSY_POLL_BUDGET);
+	return false;
+}
+
+static bool
+dynamic_tracking_do_busy_loop(struct io_ring_ctx *ctx,
+			      bool (*loop_end)(void *, unsigned long),
+			      void *loop_end_arg)
 {
 	struct io_napi_entry *e;
 	bool is_stale = false;
@@ -154,6 +191,16 @@ static bool __io_napi_do_busy_loop(struct io_ring_ctx *ctx,
 	return is_stale;
 }
 
+static inline bool
+__io_napi_do_busy_loop(struct io_ring_ctx *ctx,
+		       bool (*loop_end)(void *, unsigned long),
+		       void *loop_end_arg)
+{
+	if (READ_ONCE(ctx->napi_track_mode) == IO_URING_NAPI_TRACKING_STATIC)
+		return static_tracking_do_busy_loop(ctx, loop_end, loop_end_arg);
+	return dynamic_tracking_do_busy_loop(ctx, loop_end, loop_end_arg);
+}
+
 static void io_napi_blocking_busy_loop(struct io_ring_ctx *ctx,
 				       struct io_wait_queue *iowq)
 {
@@ -195,6 +242,7 @@ void io_napi_init(struct io_ring_ctx *ctx)
 	spin_lock_init(&ctx->napi_lock);
 	ctx->napi_prefer_busy_poll = false;
 	ctx->napi_busy_poll_dt = ns_to_ktime(sys_dt);
+	ctx->napi_track_mode = IO_URING_NAPI_TRACKING_INACTIVE;
 }
 
 /*
@@ -215,6 +263,24 @@ void io_napi_free(struct io_ring_ctx *ctx)
 	INIT_LIST_HEAD_RCU(&ctx->napi_list);
 }
 
+static int io_napi_register_napi(struct io_ring_ctx *ctx,
+				 struct io_uring_napi *napi)
+{
+	switch (napi->op_param) {
+	case IO_URING_NAPI_TRACKING_DYNAMIC:
+	case IO_URING_NAPI_TRACKING_STATIC:
+		break;
+	default:
+		return -EINVAL;
+	}
+	/* clean the napi list for new settings */
+	io_napi_free(ctx);
+	WRITE_ONCE(ctx->napi_track_mode, napi->op_param);
+	WRITE_ONCE(ctx->napi_busy_poll_dt, napi->busy_poll_to * NSEC_PER_USEC);
+	WRITE_ONCE(ctx->napi_prefer_busy_poll, !!napi->prefer_busy_poll);
+	return 0;
+}
+
 /*
  * io_napi_register() - Register napi with io-uring
  * @ctx: pointer to io-uring context structure
@@ -226,7 +292,8 @@ int io_register_napi(struct io_ring_ctx *ctx, void __user *arg)
 {
 	const struct io_uring_napi curr = {
 		.busy_poll_to 	  = ktime_to_us(ctx->napi_busy_poll_dt),
-		.prefer_busy_poll = ctx->napi_prefer_busy_poll
+		.prefer_busy_poll = ctx->napi_prefer_busy_poll,
+		.op_param	  = ctx->napi_track_mode
 	};
 	struct io_uring_napi napi;
 
@@ -234,16 +301,26 @@ int io_register_napi(struct io_ring_ctx *ctx, void __user *arg)
 		return -EINVAL;
 	if (copy_from_user(&napi, arg, sizeof(napi)))
 		return -EFAULT;
-	if (napi.pad[0] || napi.pad[1] || napi.pad[2] || napi.resv)
+	if (napi.pad[0] || napi.pad[1] || napi.resv)
 		return -EINVAL;
 
 	if (copy_to_user(arg, &curr, sizeof(curr)))
 		return -EFAULT;
 
-	WRITE_ONCE(ctx->napi_busy_poll_dt, napi.busy_poll_to * NSEC_PER_USEC);
-	WRITE_ONCE(ctx->napi_prefer_busy_poll, !!napi.prefer_busy_poll);
-	WRITE_ONCE(ctx->napi_enabled, true);
-	return 0;
+	switch (napi.opcode) {
+	case IO_URING_NAPI_REGISTER_OP:
+		return io_napi_register_napi(ctx, &napi);
+	case IO_URING_NAPI_STATIC_ADD_ID:
+		if (curr.op_param != IO_URING_NAPI_TRACKING_STATIC)
+			return -EINVAL;
+		return __io_napi_add_id(ctx, napi.op_param);
+	case IO_URING_NAPI_STATIC_DEL_ID:
+		if (curr.op_param != IO_URING_NAPI_TRACKING_STATIC)
+			return -EINVAL;
+		return __io_napi_del_id(ctx, napi.op_param);
+	default:
+		return -EINVAL;
+	}
 }
 
 /*
@@ -266,7 +343,7 @@ int io_unregister_napi(struct io_ring_ctx *ctx, void __user *arg)
 
 	WRITE_ONCE(ctx->napi_busy_poll_dt, 0);
 	WRITE_ONCE(ctx->napi_prefer_busy_poll, false);
-	WRITE_ONCE(ctx->napi_enabled, false);
+	WRITE_ONCE(ctx->napi_track_mode, IO_URING_NAPI_TRACKING_INACTIVE);
 	return 0;
 }
 
diff --git a/io_uring/napi.h b/io_uring/napi.h
index 4ae622f37b30..fa742f42e09b 100644
--- a/io_uring/napi.h
+++ b/io_uring/napi.h
@@ -44,7 +44,7 @@ static inline void io_napi_add(struct io_kiocb *req)
 	struct io_ring_ctx *ctx = req->ctx;
 	struct socket *sock;
 
-	if (!READ_ONCE(ctx->napi_enabled))
+	if (READ_ONCE(ctx->napi_track_mode) != IO_URING_NAPI_TRACKING_DYNAMIC)
 		return;
 
 	sock = sock_from_file(req->file);
-- 
2.47.0

Re: [PATCH v4 0/6] napi tracking strategy

[Jens Axboe]

On Sun, 13 Oct 2024 14:28:05 -0400, Olivier Langlois wrote:
> the actual napi tracking strategy is inducing a non-negligeable overhead.
> Everytime a multishot poll is triggered or any poll armed, if the napi is
> enabled on the ring a lookup is performed to either add a new napi id into
> the napi_list or its timeout value is updated.
> 
> For many scenarios, this is overkill as the napi id list will be pretty
> much static most of the time. To address this common scenario, the concept of io_uring_napi_tracking_strategy has been created.
> the tracking strategy can be specified when io_register_napi() is called.
> 
> [...]

Applied, thanks!

[1/6] io_uring/napi: protect concurrent io_napi_entry timeout accesses
      commit: d54db33e51090f68645fecb252a3ad22f28512cf
[2/6] io_uring/napi: fix io_napi_entry RCU accesses
      commit: 613dbde4863699fe88e601ddd7315f04c1aa3239
[3/6] io_uring/napi: improve __io_napi_add
      commit: e17bd6f1106d8c45e186a52d3ac0412f17e657c3
[4/6] io_uring/napi: Use lock guards
      commit: 6710c043c8e9d8fa9649fffd8855e3ad883bf001
[5/6] io_uring/napi: clean up __io_napi_do_busy_loop
      commit: c596060fbe5a1c094d46d8f7191a866879fe6672
[6/6] io_uring/napi: add static napi tracking strategy
      commit: cc909543d239912669b14250e796bbd877f8128a

Best regards,
-- 
Jens Axboe

Re: [PATCH v4 0/6] napi tracking strategy

[Jens Axboe]

On 11/4/24 10:49 AM, Jens Axboe wrote:
> 
> On Sun, 13 Oct 2024 14:28:05 -0400, Olivier Langlois wrote:
>> the actual napi tracking strategy is inducing a non-negligeable overhead.
>> Everytime a multishot poll is triggered or any poll armed, if the napi is
>> enabled on the ring a lookup is performed to either add a new napi id into
>> the napi_list or its timeout value is updated.
>>
>> For many scenarios, this is overkill as the napi id list will be pretty
>> much static most of the time. To address this common scenario, the concept of io_uring_napi_tracking_strategy has been created.
>> the tracking strategy can be specified when io_register_napi() is called.
>>
>> [...]
> 
> Applied, thanks!
> 
> [1/6] io_uring/napi: protect concurrent io_napi_entry timeout accesses
>       commit: d54db33e51090f68645fecb252a3ad22f28512cf
> [2/6] io_uring/napi: fix io_napi_entry RCU accesses
>       commit: 613dbde4863699fe88e601ddd7315f04c1aa3239
> [3/6] io_uring/napi: improve __io_napi_add
>       commit: e17bd6f1106d8c45e186a52d3ac0412f17e657c3
> [4/6] io_uring/napi: Use lock guards
>       commit: 6710c043c8e9d8fa9649fffd8855e3ad883bf001
> [5/6] io_uring/napi: clean up __io_napi_do_busy_loop
>       commit: c596060fbe5a1c094d46d8f7191a866879fe6672
> [6/6] io_uring/napi: add static napi tracking strategy
>       commit: cc909543d239912669b14250e796bbd877f8128a

Finally got around to this one, apologies for the delay. It looks really
nice at this point.

I'm assuming you have a liburing branch too, with the new register parts
documented, and probably helpers for setting it up? Would be nice to have
an addition to the napi test case as well, so this can get exercised as
part of the usual testing.

-- 
Jens Axboe