[PATCH net-next] sock: add sndbuff full perf trace event

[Joe Damato <jdamato@fastly.com>]

Calls to sock_alloc_send_pskb can fail or trigger a wait if there is no
sndbuf space available.

Add a perf trace event to help users monitor when and how this occurs so
appropriate application level changes can be made, if necessary.

Signed-off-by: Joe Damato <jdamato@fastly.com>
---
 include/trace/events/sock.h | 21 +++++++++++++++++++++
 net/core/sock.c             |  1 +
 2 files changed, 22 insertions(+)

diff --git a/include/trace/events/sock.h b/include/trace/events/sock.h
index 12c3157..de6f6a7 100644
--- a/include/trace/events/sock.h
+++ b/include/trace/events/sock.h
@@ -68,6 +68,27 @@ skmem_kind_names
 #define show_skmem_kind_names(val)	\
 	__print_symbolic(val, skmem_kind_names)
 
+TRACE_EVENT(sock_sndbuf_full,
+	TP_PROTO(struct sock *sk, long timeo),
+
+	TP_ARGS(sk, timeo),
+
+	TP_STRUCT__entry(
+		__field(int, wmem_alloc)
+		__field(int, sk_sndbuf)
+		__field(long, timeo)
+	),
+
+	TP_fast_assign(
+		__entry->wmem_alloc = refcount_read(&sk->sk_wmem_alloc);
+		__entry->sk_sndbuf = READ_ONCE(sk->sk_sndbuf);
+		__entry->timeo = timeo;
+	),
+
+	TP_printk("wmem_alloc=%d sk_sndbf=%d timeo=%ld",
+		__entry->wmem_alloc, __entry->sk_sndbuf, __entry->timeo)
+);
+
 TRACE_EVENT(sock_rcvqueue_full,
 
 	TP_PROTO(struct sock *sk, struct sk_buff *skb),
diff --git a/net/core/sock.c b/net/core/sock.c
index e21485a..674627c 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -2571,6 +2571,7 @@ struct sk_buff *sock_alloc_send_pskb(struct sock *sk, unsigned long header_len,
 
 		sk_set_bit(SOCKWQ_ASYNC_NOSPACE, sk);
 		set_bit(SOCK_NOSPACE, &sk->sk_socket->flags);
+		trace_sock_sndbuf_full(sk, timeo);
 		err = -EAGAIN;
 		if (!timeo)
 			goto failure;
-- 
2.7.4