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Neal Cardwell 5ae344c949 tcp: reduce spurious retransmits due to transient SACK reneging 
This commit reduces spurious retransmits due to apparent SACK reneging
by only reacting to SACK reneging that persists for a short delay.

When a sequence space hole at snd_una is filled, some TCP receivers
send a series of ACKs as they apparently scan their out-of-order queue
and cumulatively ACK all the packets that have now been consecutiveyly
received. This is essentially misbehavior B in "Misbehaviors in TCP
SACK generation" ACM SIGCOMM Computer Communication Review, April
2011, so we suspect that this is from several common OSes (Windows
2000, Windows Server 2003, Windows XP). However, this issue has also
been seen in other cases, e.g. the netdev thread "TCP being hoodwinked
into spurious retransmissions by lack of timestamps?" from March 2014,
where the receiver was thought to be a BSD box.

Since snd_una would temporarily be adjacent to a previously SACKed
range in these scenarios, this receiver behavior triggered the Linux
SACK reneging code path in the sender. This led the sender to clear
the SACK scoreboard, enter CA_Loss, and spuriously retransmit
(potentially) every packet from the entire write queue at line rate
just a few milliseconds before the ACK for each packet arrives at the
sender.

To avoid such situations, now when a sender sees apparent reneging it
does not yet retransmit, but rather adjusts the RTO timer to give the
receiver a little time (max(RTT/2, 10ms)) to send us some more ACKs
that will restore sanity to the SACK scoreboard. If the reneging
persists until this RTO then, as before, we clear the SACK scoreboard
and enter CA_Loss.

A 10ms delay tolerates a receiver sending such a stream of ACKs at
56Kbit/sec. And to allow for receivers with slower or more congested
paths, we wait for at least RTT/2.

We validated the resulting max(RTT/2, 10ms) delay formula with a mix
of North American and South American Google web server traffic, and
found that for ACKs displaying transient reneging:

 (1) 90% of inter-ACK delays were less than 10ms
 (2) 99% of inter-ACK delays were less than RTT/2

In tests on Google web servers this commit reduced reneging events by
75%-90% (as measured by the TcpExtTCPSACKReneging counter), without
any measurable impact on latency for user HTTP and SPDY requests.

Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
2014-08-05 16:29:33 -07:00
..
9p 9pnet: p9_client->conn field is unused. Remove it. 2014-03-25 16:38:16 -05:00
bluetooth Bluetooth: Rename pairable mgmt setting to bondable 2014-07-30 19:28:41 +02:00
caif caif_hsi.h: Remove extern from function prototypes 2013-09-23 16:29:41 -04:00
irda include/net/: Fix FSF address in file headers 2013-12-06 12:37:56 -05:00
iucv
netfilter Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2014-07-22 00:44:59 -07:00
netns netfilter: kill remnants of ulog targets 2014-07-25 14:55:44 +02:00
nfc NFC: digital: Add 'tg_listen_md' and 'tg_get_rf_tech' driver hooks 2014-07-23 01:17:31 +02:00
phonet
sctp sctp: Fixup v4mapped behaviour to comply with Sock API 2014-07-31 21:49:06 -07:00
tc_act net_sched: act: hide struct tcf_common from API 2014-02-12 19:23:32 -05:00
6lowpan.h 6lowpan: remove unused function 2014-07-30 19:28:41 +02:00
act_api.h net_sched: act: refuse to remove bound action outside 2014-02-12 19:23:32 -05:00
addrconf.h net: ipv6: Introduce ip6_sk_dst_hoplimit. 2014-04-30 13:31:26 -04:00
af_ieee802154.h ieee802154: add dgram sockopts for security control 2014-05-16 17:23:41 -04:00
af_rxrpc.h
af_unix.h
af_vsock.h vsock: Make transport the proto owner 2014-05-05 13:13:50 -04:00
ah.h
arp.h arp: make arp_invalidate static 2013-12-28 17:02:46 -05:00
atmclip.h
ax25.h
ax88796.h
busy_poll.h sched, net: Fixup busy_loop_us_clock() 2014-01-13 17:39:11 +01:00
cfg80211-wext.h
cfg80211.h cfg80211: remove channel_switch combination check 2014-06-25 18:06:20 +02:00
checksum.h net: Allow csum_add to be provided in arch 2014-05-05 15:26:29 -04:00
cipso_ipv4.h cipso: cleanup cipso_v4_translate() when !CONFIG_NETLABEL 2013-12-10 17:56:54 -05:00
cls_cgroup.h cgroup: clean up cgroup_subsys names and initialization 2014-02-08 10:36:58 -05:00
codel.h net: introduce reciprocal_scale helper and convert users 2014-01-21 23:17:20 -08:00
compat.h compat.h: Remove extern from function prototypes 2013-09-20 14:49:32 -04:00
datalink.h net: Move prototype declaration to header file include/net/datalink.h from net/ipx/af_ipx.c 2014-02-09 17:32:50 -08:00
dcbevent.h include/net/: Fix FSF address in file headers 2013-12-06 12:37:56 -05:00
dcbnl.h Update setapp/getapp prototypes in dcbnl_rtnl_ops to return int instead of u8 2014-07-17 16:02:29 -07:00
dn.h net: Move prototype declaration to header file include/net/dn.h from net/decnet/af_decnet.c 2014-02-09 17:32:49 -08:00
dn_dev.h dn_dev: add support for IFA_FLAGS nl attribute 2013-12-10 21:50:00 -05:00
dn_fib.h decnet (dn*.h): Remove extern from function prototypes 2013-09-20 14:49:32 -04:00
dn_neigh.h decnet (dn*.h): Remove extern from function prototypes 2013-09-20 14:49:32 -04:00
dn_nsp.h decnet (dn*.h): Remove extern from function prototypes 2013-09-20 14:49:32 -04:00
dn_route.h net: Move prototype declaration to appropriate header file from decnet/af_decnet.c 2014-02-09 17:32:49 -08:00
dsa.h net: dsa: add ds_to_priv 2014-04-30 13:31:25 -04:00
dsfield.h
dst.h ipv4: add a sock pointer to dst->output() path. 2014-04-15 13:47:15 -04:00
dst_ops.h
esp.h net: move pskb_put() to core code 2013-11-07 19:28:58 -05:00
ethoc.h net: ethoc: set up MII management bus clock 2014-02-04 20:19:51 -08:00
fib_rules.h fib_rules.h: Remove extern from function prototypes 2013-09-20 14:49:33 -04:00
firewire.h
flow.h ipv4, fib: pass LOOPBACK_IFINDEX instead of 0 to flowi4_iif 2014-04-16 15:05:11 -04:00
flow_keys.h flow_dissector: Abstract out hash computation 2014-07-07 21:14:20 -07:00
flowcache.h flowcache: Make flow cache name space aware 2014-02-12 07:02:11 +01:00
garp.h garp.h: Remove extern from function prototypes 2013-09-20 14:49:33 -04:00
gen_stats.h gen_stats.h: Remove extern from function prototypes 2013-09-20 14:49:33 -04:00
genetlink.h genl: Add genlmsg_new_unicast() for unicast message allocation 2014-01-06 15:51:53 -08:00
gre.h gre: Call gso_make_checksum 2014-06-04 22:46:38 -07:00
gro_cells.h
icmp.h icmp.h: Remove extern from function prototypes 2013-09-20 14:49:33 -04:00
ieee80211_radiotap.h mac80211: propagate STBC / LDPC flags to radiotap 2014-02-06 09:34:58 +01:00
ieee802154.h ieee802154: add definitions for link-layer security and header functions 2014-05-15 15:51:42 -04:00
ieee802154_netdev.h ieee802154, mac802154: implement devkey record option 2014-05-16 17:23:42 -04:00
if_inet6.h ipv6: addrconf: implement address generation modes 2014-07-11 15:05:45 -07:00
inet6_connection_sock.h ipv4: add a sock pointer to ip_queue_xmit() 2014-04-15 12:58:34 -04:00
inet6_hashtables.h ipv6: split inet6_ehashfn to hash functions per compilation unit 2013-10-19 19:45:34 -04:00
inet_common.h inet*.h: Remove extern from function prototypes 2013-09-21 14:01:38 -04:00
inet_connection_sock.h ipv4: add a sock pointer to ip_queue_xmit() 2014-04-15 12:58:34 -04:00
inet_ecn.h tunnel: fix RFC number in comment for INET_ECN_decapsulate() 2014-05-07 15:30:52 -04:00
inet_frag.h inet: frags: use kmem_cache for inet_frag_queue 2014-08-02 15:31:31 -07:00
inet_hashtables.h net: Use a more standard macro for INET_ADDR_COOKIE 2014-05-14 16:07:23 -04:00
inet_sock.h net: remove inet6_reqsk_alloc 2014-06-27 15:53:35 -07:00
inet_timewait_sock.h inet: move ipv6only in sock_common 2014-07-01 23:46:21 -07:00
inetpeer.h Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2014-06-03 23:32:12 -07:00
ip.h Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2014-07-30 13:25:49 -07:00
ip6_checksum.h udp: Generic functions to set checksum 2014-06-04 22:46:38 -07:00
ip6_fib.h ipv6: do not overwrite inetpeer metrics prematurely 2014-03-27 15:09:07 -04:00
ip6_route.h Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2014-05-24 00:32:30 -04:00
ip6_tunnel.h net: unify the pcpu_tstats and br_cpu_netstats as one 2014-01-04 20:10:24 -05:00
ip_fib.h ip*.h: Remove extern from function prototypes 2013-09-21 14:01:38 -04:00
ip_tunnels.h ipv4: add a sock pointer to dst->output() path. 2014-04-15 13:47:15 -04:00
ip_vs.h arch: Mass conversion of smp_mb__*() 2014-04-18 14:20:48 +02:00
ipcomp.h
ipconfig.h
ipv6.h inet: frag: don't account number of fragment queues 2014-07-27 22:34:36 -07:00
ipx.h net: Move prototype declaration to header file include/net/ipx.h from net/ipx/af_ipx.c 2014-02-09 17:32:50 -08:00
iw_handler.h iw_handler.h: Remove extern from function prototypes 2013-09-21 14:01:39 -04:00
lapb.h lapb.h: Remove extern from function prototypes 2013-09-21 14:01:38 -04:00
lib80211.h
llc.h llc: make lock static 2014-01-03 20:56:48 -05:00
llc_c_ac.h llc*.h: Remove extern from function prototypes 2013-09-21 14:01:38 -04:00
llc_c_ev.h llc*.h: Remove extern from function prototypes 2013-09-21 14:01:38 -04:00
llc_c_st.h
llc_conn.h llc*.h: Remove extern from function prototypes 2013-09-21 14:01:38 -04:00
llc_if.h llc*.h: Remove extern from function prototypes 2013-09-21 14:01:38 -04:00
llc_pdu.h net: llc: fix order of evaluation in llc_conn_ac_inc_vr_by_1 2014-01-01 22:22:43 -05:00
llc_s_ac.h llc*.h: Remove extern from function prototypes 2013-09-21 14:01:38 -04:00
llc_s_ev.h llc*.h: Remove extern from function prototypes 2013-09-21 14:01:38 -04:00
llc_s_st.h
llc_sap.h llc*.h: Remove extern from function prototypes 2013-09-21 14:01:38 -04:00
mac80211.h mac80211: add support for Rx reordering offloading 2014-07-21 17:42:07 +02:00
mac802154.h mac802154: at86rf230: add hw flags and merge ops 2014-07-07 21:29:24 -07:00
mip6.h include/net/: Fix FSF address in file headers 2013-12-06 12:37:56 -05:00
mld.h
mrp.h Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2013-10-01 17:06:14 -04:00
ndisc.h ndisc.h: Remove extern from function prototypes 2013-09-21 14:01:39 -04:00
neighbour.h neigh: sysctl - simplify address calculation of gc_* variables 2014-07-14 14:32:51 -07:00
net_namespace.h 6lowpan: nuke net_ieee802154_lowpan() accessor when 6lowpan is disabled 2014-04-24 12:36:00 -04:00
net_ratelimit.h
netdma.h
netevent.h netevent/netlink.h: Remove extern from function prototypes 2013-09-21 14:01:39 -04:00
netlabel.h Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next 2014-01-25 11:17:34 -08:00
netlink.h netlink: Fix shadow warning on jiffies 2014-07-28 17:20:43 -07:00
netprio_cgroup.h cgroup: clean up cgroup_subsys names and initialization 2014-02-08 10:36:58 -05:00
netrom.h netrom.h: Remove extern from function prototypes 2013-09-21 14:01:39 -04:00
nexthop.h
nl802154.h ieee802154: use ieee802154_addr instead of *_sa variants 2014-03-14 22:15:26 -04:00
p8022.h p8022.h: Remove extern from function prototypes 2013-09-21 14:01:39 -04:00
ping.h ipv6: make IPV6_RECVPKTINFO work for ipv4 datagrams 2014-01-19 19:53:18 -08:00
pkt_cls.h sched, cls: check if we could overwrite actions when changing a filter 2014-04-27 23:42:39 -04:00
pkt_sched.h net_sched: drr: warn when qdisc is not work conserving 2014-06-11 15:50:59 -07:00
protocol.h net: Eliminate no_check from protosw 2014-05-23 16:28:53 -04:00
psnap.h psnap.h: Remove extern from function prototypes 2013-09-23 01:51:08 -04:00
raw.h raw/rawv6.h: Remove extern from function prototypes 2013-09-23 01:51:08 -04:00
rawv6.h raw/rawv6.h: Remove extern from function prototypes 2013-09-23 01:51:08 -04:00
red.h reciprocal_divide: update/correction of the algorithm 2014-01-21 23:17:20 -08:00
regulatory.h cfg80211: Enable GO operation on additional channels 2014-04-09 10:55:34 +02:00
request_sock.h inet: includes a sock_common in request_sock 2013-10-10 00:08:07 -04:00
rose.h rose.h: Remove extern from function prototypes 2013-09-23 01:51:08 -04:00
route.h ipv4: remove ip_rt_dump from route.c 2014-03-24 12:45:01 -04:00
rtnetlink.h net: rtnetlink - make create_link take name_assign_type 2014-07-15 16:13:07 -07:00
sch_generic.h flow_keys: Record IP layer protocol in skb_flow_dissect() 2014-06-23 14:32:19 -07:00
scm.h scm.h: Remove extern from function prototypes 2013-09-23 01:51:09 -04:00
secure_seq.h inetpeer: get rid of ip_id_count 2014-06-02 11:00:41 -07:00
slhc_vj.h
snmp.h net: clean up snmp stats code 2014-05-07 16:06:05 -04:00
sock.h net: remove deprecated syststamp timestamp 2014-07-29 11:39:50 -07:00
Space.h drivers: net: Include new header file in sbni.c 2013-12-19 18:51:20 -05:00
stp.h stp.h: Remove extern from function prototypes 2013-09-23 01:51:09 -04:00
tcp.h tcp: reduce spurious retransmits due to transient SACK reneging 2014-08-05 16:29:33 -07:00
tcp_memcontrol.h tcp_memcontrol: Kill struct tcp_memcontrol 2013-10-21 18:43:02 -04:00
tcp_states.h
timewait_sock.h
transp_v6.h ipv6: make IPV6_RECVPKTINFO work for ipv4 datagrams 2014-01-19 19:53:18 -08:00
tso.h net: Add a software TSO helper API 2014-05-22 14:57:15 -04:00
udp.h udp: Add function to make source port for UDP tunnels 2014-07-07 21:14:21 -07:00
udp_tunnel.h udp: Add udp_sock_create for UDP tunnels to open listener socket 2014-07-14 16:12:15 -07:00
udplite.h udplite.h: Remove extern from function prototypes 2013-09-23 16:29:40 -04:00
vsock_addr.h
vxlan.h vxlan: Call udp_flow_src_port 2014-07-07 21:14:21 -07:00
wext.h wext.h: Remove extern from function prototypes 2013-09-23 16:29:40 -04:00
wimax.h wimax: Spelling s/than/that/, wording s/destinatary/recipient/ 2014-05-05 15:37:55 +02:00
wpan-phy.h ieee802154: add netlink APIs for smartMAC configuration 2014-02-17 16:42:39 -05:00
x25.h x25.h: Remove extern from function prototypes 2013-09-23 16:29:41 -04:00
x25device.h
xfrm.h xfrm: Remove useless xfrm_audit struct. 2014-04-23 08:21:04 +02:00