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| author | Eric Dumazet <edumazet@google.com> | 2013-04-18 06:52:51 +0000 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2013-04-18 14:57:25 -0400 |
| commit | 0e280af026a5662ffd57c4e623b822df1f7f47ff (patch) | |
| tree | ee3fa2a5523223f8ff079b075dc4e1959ed0c0f5 /net/ipv4 | |
| parent | 5a5967d80423e859036972986b3711458f2cd385 (diff) | |
| download | linux-0-day-0e280af026a5662ffd57c4e623b822df1f7f47ff.tar.gz linux-0-day-0e280af026a5662ffd57c4e623b822df1f7f47ff.tar.xz | |
tcp: introduce TCPSpuriousRtxHostQueues SNMP counter
Host queues (Qdisc + NIC) can hold packets so long that TCP can
eventually retransmit a packet before the first transmit even left
the host.
Its not clear right now if we could avoid this in the first place :
- We could arm RTO timer not at the time we enqueue packets, but
at the time we TX complete them (tcp_wfree())
- Cancel the sending of the new copy of the packet if prior one
is still in queue.
This patch adds instrumentation so that we can at least see how
often this problem happens.
TCPSpuriousRtxHostQueues SNMP counter is incremented every time
we detect the fast clone is not yet freed in tcp_transmit_skb()
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Cc: Tom Herbert <therbert@google.com>
Cc: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/ipv4')
| -rw-r--r-- | net/ipv4/proc.c | 1 | ||||
| -rw-r--r-- | net/ipv4/tcp_output.c | 7 |
2 files changed, 8 insertions, 0 deletions
diff --git a/net/ipv4/proc.c b/net/ipv4/proc.c index b6f2ea1748988..6da51d55d03a1 100644 --- a/net/ipv4/proc.c +++ b/net/ipv4/proc.c @@ -269,6 +269,7 @@ static const struct snmp_mib snmp4_net_list[] = { SNMP_MIB_ITEM("TCPFastOpenPassiveFail", LINUX_MIB_TCPFASTOPENPASSIVEFAIL), SNMP_MIB_ITEM("TCPFastOpenListenOverflow", LINUX_MIB_TCPFASTOPENLISTENOVERFLOW), SNMP_MIB_ITEM("TCPFastOpenCookieReqd", LINUX_MIB_TCPFASTOPENCOOKIEREQD), + SNMP_MIB_ITEM("TCPSpuriousRtxHostQueues", LINUX_MIB_TCPSPURIOUS_RTX_HOSTQUEUES), SNMP_MIB_SENTINEL }; diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index d126943535405..5f28131eb37e3 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -846,6 +846,13 @@ static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it, __net_timestamp(skb); if (likely(clone_it)) { + const struct sk_buff *fclone = skb + 1; + + if (unlikely(skb->fclone == SKB_FCLONE_ORIG && + fclone->fclone == SKB_FCLONE_CLONE)) + NET_INC_STATS_BH(sock_net(sk), + LINUX_MIB_TCPSPURIOUS_RTX_HOSTQUEUES); + if (unlikely(skb_cloned(skb))) skb = pskb_copy(skb, gfp_mask); else |