[PATCH v2 net-next] net: introduce a new tracepoint for tcp_rcv_space_adjust

[Yafang Shao]

tcp_rcv_space_adjust is called every time data is copied to user space,
introducing a tcp tracepoint for which could show us when the packet is
copied to user.
This could help us figure out whether there's latency in user process.

When a tcp packet arrives, tcp_rcv_established() will be called and with
the existed tracepoint tcp_probe we could get the time when this packet
arrives.
Then this packet will be copied to user, and tcp_rcv_space_adjust will
be called and with this new introduced tracepoint we could get the time
when this packet is copied to user.

        arrives time : user process time    => latency caused by user
        tcp_probe      tcp_rcv_space_adjust

Hence in the printk message, sk_cookie is printed as a key to relate
tcp_rcv_space_adjust with tcp_probe.

Maybe we could export sockfd in this new tracepoint as well, then we
could relate this new tracepoint with epoll/read/recv* tracepoints, and
finally that could show us the whole lifespan of this packet. But we
could also implement that with pid as these functions are executed in
process context.

Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>

---
v1 -> v2: use sk_cookie as key suggested by Eric.
---
 include/trace/events/tcp.h | 33 +++++++++++++++++++++++++++------
 net/ipv4/tcp_input.c       |  2 ++
 2 files changed, 29 insertions(+), 6 deletions(-)

diff --git a/include/trace/events/tcp.h b/include/trace/events/tcp.h
index 3dd6802..814f754 100644
--- a/include/trace/events/tcp.h
+++ b/include/trace/events/tcp.h
@@ -10,6 +10,7 @@
 #include <linux/tracepoint.h>
 #include <net/ipv6.h>
 #include <net/tcp.h>
+#include <linux/sock_diag.h>
 
 #define TP_STORE_V4MAPPED(__entry, saddr, daddr)		\
 	do {							\
@@ -125,6 +126,7 @@
 		__array(__u8, daddr, 4)
 		__array(__u8, saddr_v6, 16)
 		__array(__u8, daddr_v6, 16)
+		__field(__u64, sock_cookie)
 	),
 
 	TP_fast_assign(
@@ -144,12 +146,24 @@
 
 		TP_STORE_ADDRS(__entry, inet->inet_saddr, inet->inet_daddr,
 			       sk->sk_v6_rcv_saddr, sk->sk_v6_daddr);
+
+		/*
+		 * sk_cookie is used to identify a socket, with which we could
+		 * relate this tracepoint with other tracepoints,
+		 * i.e. tcp_probe.
+		 * If we needn't this relation, then sk_cookie is useless;
+		 * if we need this relation, then tcp_probe is already set,
+		 * and sk_cookie is already set in tcp_probe, so we could get
+		 * the value directly.
+		 */
+		__entry->sock_cookie = atomic64_read(&sk->sk_cookie);
 	),
 
-	TP_printk("sport=%hu dport=%hu saddr=%pI4 daddr=%pI4 saddrv6=%pI6c daddrv6=%pI6c",
+	TP_printk("sport=%hu dport=%hu saddr=%pI4 daddr=%pI4 saddrv6=%pI6c daddrv6=%pI6c sock_cookie=%llu",
 		  __entry->sport, __entry->dport,
 		  __entry->saddr, __entry->daddr,
-		  __entry->saddr_v6, __entry->daddr_v6)
+		  __entry->saddr_v6, __entry->daddr_v6,
+		  __entry->sock_cookie)
 );
 
 DEFINE_EVENT(tcp_event_sk, tcp_receive_reset,
@@ -166,6 +180,13 @@
 	TP_ARGS(sk)
 );
 
+DEFINE_EVENT(tcp_event_sk, tcp_rcv_space_adjust,
+
+	TP_PROTO(const struct sock *sk),
+
+	TP_ARGS(sk)
+);
+
 TRACE_EVENT(tcp_retransmit_synack,
 
 	TP_PROTO(const struct sock *sk, const struct request_sock *req),
@@ -232,6 +253,7 @@
 		__field(__u32, snd_wnd)
 		__field(__u32, srtt)
 		__field(__u32, rcv_wnd)
+		__field(__u64, sock_cookie)
 	),
 
 	TP_fast_assign(
@@ -256,15 +278,14 @@
 		__entry->rcv_wnd = tp->rcv_wnd;
 		__entry->ssthresh = tcp_current_ssthresh(sk);
 		__entry->srtt = tp->srtt_us >> 3;
+		__entry->sock_cookie = sock_gen_cookie(sk);
 	),
 
-	TP_printk("src=%pISpc dest=%pISpc mark=%#x length=%d snd_nxt=%#x "
-		  "snd_una=%#x snd_cwnd=%u ssthresh=%u snd_wnd=%u srtt=%u "
-		  "rcv_wnd=%u",
+	TP_printk("src=%pISpc dest=%pISpc mark=%#x length=%d snd_nxt=%#x snd_una=%#x snd_cwnd=%u ssthresh=%u snd_wnd=%u srtt=%u rcv_wnd=%u sock_cookie=%llu",
 		  __entry->saddr, __entry->daddr, __entry->mark,
 		  __entry->length, __entry->snd_nxt, __entry->snd_una,
 		  __entry->snd_cwnd, __entry->ssthresh, __entry->snd_wnd,
-		  __entry->srtt, __entry->rcv_wnd)
+		  __entry->srtt, __entry->rcv_wnd, __entry->sock_cookie)
 );
 
 #endif /* _TRACE_TCP_H */
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index f93687f..43ad468 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -582,6 +582,8 @@ void tcp_rcv_space_adjust(struct sock *sk)
 	u32 copied;
 	int time;
 
+	trace_tcp_rcv_space_adjust(sk);
+
 	tcp_mstamp_refresh(tp);
 	time = tcp_stamp_us_delta(tp->tcp_mstamp, tp->rcvq_space.time);
 	if (time < (tp->rcv_rtt_est.rtt_us >> 3) || tp->rcv_rtt_est.rtt_us == 0)
-- 
1.8.3.1