[net-next,v2] tcp: add a tracepoint for tcp_retransmit_skb()

Message ID 20171012224807.1669-1-xiyou.wangcong@gmail.com
State Superseded
Delegated to: David Miller
Headers show
Series
  • [net-next,v2] tcp: add a tracepoint for tcp_retransmit_skb()
Related show

Commit Message

Cong Wang Oct. 12, 2017, 10:48 p.m.
We need a real-time notification for tcp retransmission
for monitoring.

Of course we could use ftrace to dynamically instrument this
kernel function too, however we can't retrieve the connection
information at the same time, for example perf-tools [1] reads
/proc/net/tcp for socket details, which is slow when we have
a lots of connections.

Therefore, this patch adds a tracepoint for tcp_retransmit_skb()
and exposes src/dst IP addresses and ports of the connection.
This also makes it easier to integrate into perf.

Note, I expose both IPv4 and IPv6 addresses at the same time:
for a IPv4 socket, v4 mapped address is used as IPv6 addresses,
for a IPv6 socket, LOOPBACK4_IPV6 is already filled by kernel.
Also, add sk and skb pointers as they are useful for BPF.

1. https://github.com/brendangregg/perf-tools/blob/master/net/tcpretrans

Cc: Eric Dumazet <edumazet@google.com>
Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Hannes Frederic Sowa <hannes@stressinduktion.org>
Cc: Brendan Gregg <brendan.d.gregg@gmail.com>
Cc: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
---
 include/trace/events/tcp.h | 68 ++++++++++++++++++++++++++++++++++++++++++++++
 net/core/net-traces.c      |  1 +
 net/ipv4/tcp_output.c      |  3 ++
 3 files changed, 72 insertions(+)
 create mode 100644 include/trace/events/tcp.h

Comments

Alexei Starovoitov Oct. 12, 2017, 11:18 p.m. | #1
On Thu, Oct 12, 2017 at 03:48:07PM -0700, Cong Wang wrote:
> We need a real-time notification for tcp retransmission
> for monitoring.
> 
> Of course we could use ftrace to dynamically instrument this
> kernel function too, however we can't retrieve the connection
> information at the same time, for example perf-tools [1] reads
> /proc/net/tcp for socket details, which is slow when we have
> a lots of connections.
> 
> Therefore, this patch adds a tracepoint for tcp_retransmit_skb()
> and exposes src/dst IP addresses and ports of the connection.
> This also makes it easier to integrate into perf.
> 
> Note, I expose both IPv4 and IPv6 addresses at the same time:
> for a IPv4 socket, v4 mapped address is used as IPv6 addresses,
> for a IPv6 socket, LOOPBACK4_IPV6 is already filled by kernel.
> Also, add sk and skb pointers as they are useful for BPF.
> 
> 1. https://github.com/brendangregg/perf-tools/blob/master/net/tcpretrans
> 
> Cc: Eric Dumazet <edumazet@google.com>
> Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>
> Cc: Hannes Frederic Sowa <hannes@stressinduktion.org>
> Cc: Brendan Gregg <brendan.d.gregg@gmail.com>
> Cc: Neal Cardwell <ncardwell@google.com>
> Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
> ---
>  include/trace/events/tcp.h | 68 ++++++++++++++++++++++++++++++++++++++++++++++
>  net/core/net-traces.c      |  1 +
>  net/ipv4/tcp_output.c      |  3 ++
>  3 files changed, 72 insertions(+)
>  create mode 100644 include/trace/events/tcp.h
> 
> diff --git a/include/trace/events/tcp.h b/include/trace/events/tcp.h
> new file mode 100644
> index 000000000000..749f93c542ab
> --- /dev/null
> +++ b/include/trace/events/tcp.h
> @@ -0,0 +1,68 @@
> +#undef TRACE_SYSTEM
> +#define TRACE_SYSTEM tcp
> +
> +#if !defined(_TRACE_TCP_H) || defined(TRACE_HEADER_MULTI_READ)
> +#define _TRACE_TCP_H
> +
> +#include <linux/ipv6.h>
> +#include <linux/tcp.h>
> +#include <linux/tracepoint.h>
> +#include <net/ipv6.h>
> +
> +TRACE_EVENT(tcp_retransmit_skb,
> +
> +	TP_PROTO(struct sock *sk, struct sk_buff *skb, int segs),
> +
> +	TP_ARGS(sk, skb, segs),
> +
> +	TP_STRUCT__entry(
> +		__field(void *, skbaddr)
> +		__field(void *, skaddr)
> +		__field(__u16, sport)
> +		__field(__u16, dport)
> +		__array(__u8, saddr, 4)
> +		__array(__u8, daddr, 4)
> +		__array(__u8, saddr_v6, 16)
> +		__array(__u8, daddr_v6, 16)
> +	),
...
>  	if (likely(!err)) {
>  		TCP_SKB_CB(skb)->sacked |= TCPCB_EVER_RETRANS;
> +		trace_tcp_retransmit_skb(sk, skb, segs);

looks great to me, but why 'segs' is there?
It's unused.
Cong Wang Oct. 13, 2017, 5:33 p.m. | #2
On Thu, Oct 12, 2017 at 4:18 PM, Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
> On Thu, Oct 12, 2017 at 03:48:07PM -0700, Cong Wang wrote:
>> We need a real-time notification for tcp retransmission
>> for monitoring.
>>
>> Of course we could use ftrace to dynamically instrument this
>> kernel function too, however we can't retrieve the connection
>> information at the same time, for example perf-tools [1] reads
>> /proc/net/tcp for socket details, which is slow when we have
>> a lots of connections.
>>
>> Therefore, this patch adds a tracepoint for tcp_retransmit_skb()
>> and exposes src/dst IP addresses and ports of the connection.
>> This also makes it easier to integrate into perf.
>>
>> Note, I expose both IPv4 and IPv6 addresses at the same time:
>> for a IPv4 socket, v4 mapped address is used as IPv6 addresses,
>> for a IPv6 socket, LOOPBACK4_IPV6 is already filled by kernel.
>> Also, add sk and skb pointers as they are useful for BPF.
>>
>> 1. https://github.com/brendangregg/perf-tools/blob/master/net/tcpretrans
>>
>> Cc: Eric Dumazet <edumazet@google.com>
>> Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>
>> Cc: Hannes Frederic Sowa <hannes@stressinduktion.org>
>> Cc: Brendan Gregg <brendan.d.gregg@gmail.com>
>> Cc: Neal Cardwell <ncardwell@google.com>
>> Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
>> ---
>>  include/trace/events/tcp.h | 68 ++++++++++++++++++++++++++++++++++++++++++++++
>>  net/core/net-traces.c      |  1 +
>>  net/ipv4/tcp_output.c      |  3 ++
>>  3 files changed, 72 insertions(+)
>>  create mode 100644 include/trace/events/tcp.h
>>
>> diff --git a/include/trace/events/tcp.h b/include/trace/events/tcp.h
>> new file mode 100644
>> index 000000000000..749f93c542ab
>> --- /dev/null
>> +++ b/include/trace/events/tcp.h
>> @@ -0,0 +1,68 @@
>> +#undef TRACE_SYSTEM
>> +#define TRACE_SYSTEM tcp
>> +
>> +#if !defined(_TRACE_TCP_H) || defined(TRACE_HEADER_MULTI_READ)
>> +#define _TRACE_TCP_H
>> +
>> +#include <linux/ipv6.h>
>> +#include <linux/tcp.h>
>> +#include <linux/tracepoint.h>
>> +#include <net/ipv6.h>
>> +
>> +TRACE_EVENT(tcp_retransmit_skb,
>> +
>> +     TP_PROTO(struct sock *sk, struct sk_buff *skb, int segs),
>> +
>> +     TP_ARGS(sk, skb, segs),
>> +
>> +     TP_STRUCT__entry(
>> +             __field(void *, skbaddr)
>> +             __field(void *, skaddr)
>> +             __field(__u16, sport)
>> +             __field(__u16, dport)
>> +             __array(__u8, saddr, 4)
>> +             __array(__u8, daddr, 4)
>> +             __array(__u8, saddr_v6, 16)
>> +             __array(__u8, daddr_v6, 16)
>> +     ),
> ...
>>       if (likely(!err)) {
>>               TCP_SKB_CB(skb)->sacked |= TCPCB_EVER_RETRANS;
>> +             trace_tcp_retransmit_skb(sk, skb, segs);
>
> looks great to me, but why 'segs' is there?
> It's unused.

Ah, I copy-n-paste the tcp_retransmit_skb() prototype...
I will remove it.

Thanks.

Patch

diff --git a/include/trace/events/tcp.h b/include/trace/events/tcp.h
new file mode 100644
index 000000000000..749f93c542ab
--- /dev/null
+++ b/include/trace/events/tcp.h
@@ -0,0 +1,68 @@ 
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM tcp
+
+#if !defined(_TRACE_TCP_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_TCP_H
+
+#include <linux/ipv6.h>
+#include <linux/tcp.h>
+#include <linux/tracepoint.h>
+#include <net/ipv6.h>
+
+TRACE_EVENT(tcp_retransmit_skb,
+
+	TP_PROTO(struct sock *sk, struct sk_buff *skb, int segs),
+
+	TP_ARGS(sk, skb, segs),
+
+	TP_STRUCT__entry(
+		__field(void *, skbaddr)
+		__field(void *, skaddr)
+		__field(__u16, sport)
+		__field(__u16, dport)
+		__array(__u8, saddr, 4)
+		__array(__u8, daddr, 4)
+		__array(__u8, saddr_v6, 16)
+		__array(__u8, daddr_v6, 16)
+	),
+
+	TP_fast_assign(
+		struct ipv6_pinfo *np = inet6_sk(sk);
+		struct inet_sock *inet = inet_sk(sk);
+		struct in6_addr *pin6;
+		__be32 *p32;
+
+		__entry->skbaddr = skb;
+		__entry->skaddr = sk;
+
+		__entry->sport = ntohs(inet->inet_sport);
+		__entry->dport = ntohs(inet->inet_dport);
+
+		p32 = (__be32 *) __entry->saddr;
+		*p32 = inet->inet_saddr;
+
+		p32 = (__be32 *) __entry->daddr;
+		*p32 =  inet->inet_daddr;
+
+		if (np) {
+			pin6 = (struct in6_addr *)__entry->saddr_v6;
+			*pin6 = np->saddr;
+			pin6 = (struct in6_addr *)__entry->daddr_v6;
+			*pin6 = *(np->daddr_cache);
+		} else {
+			pin6 = (struct in6_addr *)__entry->saddr_v6;
+			ipv6_addr_set_v4mapped(inet->inet_saddr, pin6);
+			pin6 = (struct in6_addr *)__entry->daddr_v6;
+			ipv6_addr_set_v4mapped(inet->inet_daddr, pin6);
+		}
+	),
+
+	TP_printk("sport=%hu dport=%hu saddr=%pI4 daddr=%pI4 saddrv6=%pI6 daddrv6=%pI6",
+		  __entry->sport, __entry->dport, __entry->saddr, __entry->daddr,
+		  __entry->saddr_v6, __entry->daddr_v6)
+);
+
+#endif /* _TRACE_TCP_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>
diff --git a/net/core/net-traces.c b/net/core/net-traces.c
index 1132820c8e62..f4e4fa2db505 100644
--- a/net/core/net-traces.c
+++ b/net/core/net-traces.c
@@ -31,6 +31,7 @@ 
 #include <trace/events/napi.h>
 #include <trace/events/sock.h>
 #include <trace/events/udp.h>
+#include <trace/events/tcp.h>
 #include <trace/events/fib.h>
 #include <trace/events/qdisc.h>
 #if IS_ENABLED(CONFIG_IPV6)
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 696b0a168f16..e1e7410a5b60 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -42,6 +42,8 @@ 
 #include <linux/gfp.h>
 #include <linux/module.h>
 
+#include <trace/events/tcp.h>
+
 /* People can turn this off for buggy TCP's found in printers etc. */
 int sysctl_tcp_retrans_collapse __read_mostly = 1;
 
@@ -2875,6 +2877,7 @@  int __tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb, int segs)
 
 	if (likely(!err)) {
 		TCP_SKB_CB(skb)->sacked |= TCPCB_EVER_RETRANS;
+		trace_tcp_retransmit_skb(sk, skb, segs);
 	} else if (err != -EBUSY) {
 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRETRANSFAIL);
 	}