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Date:	Wed, 25 Jan 2012 15:44:20 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Hagen Paul Pfeifer <hagen@...u.net>
Cc:	Satoru Moriya <satoru.moriya@....com>, netdev@...r.kernel.org,
	davem@...emloft.net, nhorman@...driver.com, tgraf@...radead.org,
	Stephen Hemminger <stephen.hemminger@...tta.com>,
	Seiji Aguchi <seiji.aguchi@....com>
Subject: Re: [PATCH v2 0/2] Tracepoint for tcp retransmission

Le mercredi 25 janvier 2012 à 14:27 +0100, Hagen Paul Pfeifer a écrit :


> It is crazy to add everywhere new tracepoints. Systemtap is far from being
> perfect and as smooth as dtrace. But this is an example where systemtap is
> suitable and should be used.

Agreed, but last time I tried systemtap I failed miserably.
It was on a debian distro.

Anyway, it seems we lack a LINUX_MIB_TCPRETRANSFAIL counter.

"netstat -s" is an incredible universal tool.

[PATCH net-next] tcp: add LINUX_MIB_TCPRETRANSFAIL counter

It might be useful to get a counter of failed tcp_retransmit_skb()
calls.

Reported-by: Satoru Moriya <satoru.moriya@....com>
Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
---
 include/linux/snmp.h  |    1 +
 net/ipv4/proc.c       |    1 +
 net/ipv4/tcp_output.c |    4 +++-
 3 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/include/linux/snmp.h b/include/linux/snmp.h
index c1241c42..8ee8af4 100644
--- a/include/linux/snmp.h
+++ b/include/linux/snmp.h
@@ -232,6 +232,7 @@ enum
 	LINUX_MIB_TCPTIMEWAITOVERFLOW,		/* TCPTimeWaitOverflow */
 	LINUX_MIB_TCPREQQFULLDOCOOKIES,		/* TCPReqQFullDoCookies */
 	LINUX_MIB_TCPREQQFULLDROP,		/* TCPReqQFullDrop */
+	LINUX_MIB_TCPRETRANSFAIL,		/* TCPRetransFail */
 	__LINUX_MIB_MAX
 };
 
diff --git a/net/ipv4/proc.c b/net/ipv4/proc.c
index 6afc807..02d6107 100644
--- a/net/ipv4/proc.c
+++ b/net/ipv4/proc.c
@@ -256,6 +256,7 @@ static const struct snmp_mib snmp4_net_list[] = {
 	SNMP_MIB_ITEM("TCPTimeWaitOverflow", LINUX_MIB_TCPTIMEWAITOVERFLOW),
 	SNMP_MIB_ITEM("TCPReqQFullDoCookies", LINUX_MIB_TCPREQQFULLDOCOOKIES),
 	SNMP_MIB_ITEM("TCPReqQFullDrop", LINUX_MIB_TCPREQQFULLDROP),
+	SNMP_MIB_ITEM("TCPRetransFail", LINUX_MIB_TCPRETRANSFAIL),
 	SNMP_MIB_SENTINEL
 };
 
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 8c8de27..561550a 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2308,8 +2308,10 @@ begin_fwd:
 		if (sacked & (TCPCB_SACKED_ACKED|TCPCB_SACKED_RETRANS))
 			continue;
 
-		if (tcp_retransmit_skb(sk, skb))
+		if (tcp_retransmit_skb(sk, skb)) {
+			NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPRETRANSFAIL);
 			return;
+		}
 		NET_INC_STATS_BH(sock_net(sk), mib_idx);
 
 		if (inet_csk(sk)->icsk_ca_state == TCP_CA_Recovery)


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