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1b7fdd2ab5
linux/net/ipv4
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Yuchung Cheng 1b7fdd2ab5 tcp: do not use cached RTT for RTT estimation 
RTT cached in the TCP metrics are valuable for the initial timeout
because SYN RTT usually does not account for serialization delays
on low BW path.

However using it to seed the RTT estimator maybe disruptive because
other components (e.g., pacing) require the smooth RTT to be obtained
from actual connection.

The solution is to use the higher cached RTT to set the first RTO
conservatively like tcp_rtt_estimator(), but avoid seeding the other
RTT estimator variables such as srtt.  It is also a good idea to
keep RTO conservative to obtain the first RTT sample, and the
performance is insured by TCP loss probe if SYN RTT is available.

To keep the seeding formula consistent across SYN RTT and cached RTT,
the rttvar is twice the cached RTT instead of cached RTTVAR value. The
reason is because cached variation may be too small (near min RTO)
which defeats the purpose of being conservative on first RTO. However
the metrics still keep the RTT variations as they might be useful for
user applications (through ip).

Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Tested-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
2013-08-30 15:14:38 -04:00
..
netfilter netfilter: add SYNPROXY core/target 2013-08-28 00:27:54 +02:00
af_inet.c gro: remove a sparse error 2013-06-12 15:03:24 -07:00
ah4.c ipv4: properly refresh rtable entries on pmtu/redirect events 2013-06-03 00:07:42 -07:00
arp.c arp: flush arp cache on IFF_NOARP change 2013-05-28 13:11:02 -07:00
cipso_ipv4.c cipso: don't follow a NULL pointer when setsockopt() is called 2012-07-18 09:01:12 -07:00
datagram.c ipv4: Add a socket release callback for datagram sockets 2013-01-21 14:17:05 -05:00
devinet.c net: igmp: Allow user-space configuration of igmp unsolicited report interval 2013-08-09 11:27:46 -07:00
esp4.c net: esp{4,6}: fix potential MTU calculation overflows 2013-08-05 12:26:50 -07:00
fib_frontend.c netlink: fix splat in skb_clone with large messages 2013-06-27 22:44:16 -07:00
fib_lookup.h
fib_rules.c fib_rules: fix suppressor names and default values 2013-08-03 10:40:23 -07:00
fib_semantics.c ipv4: use next hop exceptions also for input routes 2013-06-28 21:27:47 -07:00
fib_trie.c fib_trie: remove potential out of bound access 2013-08-05 15:26:11 -07:00
gre_demux.c net: gre: move GSO functions to gre_offload 2013-07-03 14:37:39 -07:00
gre_offload.c gso: Update tunnel segmentation to support Tx checksum offload 2013-07-11 12:18:49 -07:00
icmp.c icmp: avoid allocating large struct on stack 2013-06-03 00:28:44 -07:00
igmp.c net: igmp: Allow user-space configuration of igmp unsolicited report interval 2013-08-09 11:27:46 -07:00
inet_connection_sock.c tcp: Remove TCPCT 2013-03-17 14:35:13 -04:00
inet_diag.c netlink: rename ssk to sk in struct netlink_skb_params 2013-04-19 14:57:56 -04:00
inet_fragment.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next 2013-07-09 18:24:39 -07:00
inet_hashtables.c inet: fix spacing in assignment 2013-07-11 12:02:39 -07:00
inet_lro.c ipv4: replace ip_fast_csum with csum_replace2 2013-03-15 09:12:25 -04:00
inet_timewait_sock.c hlist: drop the node parameter from iterators 2013-02-27 19:10:24 -08:00
inetpeer.c Merge branch 'for-3.7' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq 2012-10-02 09:54:49 -07:00
ip_forward.c ipv4: introduce rt_uses_gateway 2012-10-08 17:42:36 -04:00
ip_fragment.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2013-04-22 20:32:51 -04:00
ip_gre.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2013-08-16 15:37:26 -07:00
ip_input.c net: add SNMP counters tracking incoming ECN bits 2013-08-08 22:24:59 -07:00
ip_options.c net/ipv4: Ensure that location of timestamp option is stored 2013-03-12 05:35:39 -04:00
ip_output.c ipv4: ip_output: remove inline marking of EXPORT_SYMBOL functions 2013-05-11 16:12:44 -07:00
ip_sockglue.c net: prevent setting ttl=0 via IP_TTL 2013-01-08 17:57:10 -08:00
ip_tunnel_core.c ip_tunnel: Do not use inner ip-header-id for tunnel ip-header-id. 2013-08-13 16:52:50 -07:00
ip_tunnel.c ipip: potential race in ip_tunnel_init_net() 2013-08-25 18:39:59 -04:00
ip_vti.c ipip: add x-netns support 2013-08-15 01:00:20 -07:00
ipcomp.c ipv4: properly refresh rtable entries on pmtu/redirect events 2013-06-03 00:07:42 -07:00
ipconfig.c ipconfig: add informative timeout messages while waiting for carrier 2013-04-02 14:35:33 -04:00
ipip.c ipip: add x-netns support 2013-08-15 01:00:20 -07:00
ipmr.c ipmr: change the prototype of ip_mr_forward(). 2013-07-23 17:01:05 -07:00
Kconfig Kconfig: remove dangling references to the deleted file 2013-06-04 15:17:39 -07:00
Makefile net: gre: move GSO functions to gre_offload 2013-07-03 14:37:39 -07:00
netfilter.c netfilter: add my copyright statements 2013-04-18 20:27:55 +02:00
ping.c net: proc_fs: trivial: print UIDs as unsigned int 2013-08-15 14:37:46 -07:00
proc.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2013-08-16 15:37:26 -07:00
protocol.c ipv4: Disallow non-namespace aware protocols to register. 2013-02-05 14:42:23 -05:00
raw.c net: proc_fs: trivial: print UIDs as unsigned int 2013-08-15 14:37:46 -07:00
route.c ipv4: raise IP_MAX_MTU to theoretical limit 2013-08-20 15:05:04 -07:00
syncookies.c net: syncookies: export cookie_v4_init_sequence/cookie_v4_check 2013-08-28 00:27:44 +02:00
sysctl_net_ipv4.c tcp: TSO packets automatic sizing 2013-08-29 15:50:06 -04:00
tcp_bic.c
tcp_cong.c tcp: remove Appropriate Byte Count support 2013-02-05 14:51:16 -05:00
tcp_cubic.c tcp: cubic: fix bug in bictcp_acked() 2013-08-07 10:35:08 -07:00
tcp_diag.c
tcp_fastopen.c tcp: add server ip to encrypt cookie in fast open 2013-08-10 00:35:33 -07:00
tcp_highspeed.c
tcp_htcp.c
tcp_hybla.c tcp: bool conversions 2012-05-17 14:59:59 -04:00
tcp_illinois.c net: fix divide by zero in tcp algorithm illinois 2012-11-01 11:55:59 -04:00
tcp_input.c tcp: TSO packets automatic sizing 2013-08-29 15:50:06 -04:00
tcp_ipv4.c tcp: trivial: Remove nocache argument from tcp_v4_send_synack 2013-08-20 15:05:04 -07:00
tcp_lp.c
tcp_memcontrol.c net: tcp_memcontrol: minor: remove unused variable 2013-04-14 15:41:49 -04:00
tcp_metrics.c tcp: do not use cached RTT for RTT estimation 2013-08-30 15:14:38 -04:00
tcp_minisocks.c tcp: consolidate SYNACK RTT sampling 2013-07-22 17:53:42 -07:00
tcp_offload.c net: tcp: move GRO/GSO functions to tcp_offload 2013-06-07 14:39:05 -07:00
tcp_output.c tcp: TSO packets automatic sizing 2013-08-29 15:50:06 -04:00
tcp_probe.c net: tcp_probe: allow more advanced ingress filtering by mark 2013-08-27 15:53:34 -04:00
tcp_scalable.c
tcp_timer.c tcp: refactor F-RTO 2013-03-21 11:47:50 -04:00
tcp_vegas.c
tcp_vegas.h
tcp_veno.c
tcp_westwood.c tcp: refactor F-RTO 2013-03-21 11:47:50 -04:00
tcp_yeah.c
tcp.c tcp: TSO packets automatic sizing 2013-08-29 15:50:06 -04:00
tunnel4.c
udp_diag.c netlink: rename ssk to sk in struct netlink_skb_params 2013-04-19 14:57:56 -04:00
udp_impl.h
udp_offload.c net: udp4: move GSO functions to udp_offload 2013-06-12 00:47:25 -07:00
udp.c net: proc_fs: trivial: print UIDs as unsigned int 2013-08-15 14:37:46 -07:00
udplite.c
xfrm4_input.c net: Add skb_unclone() helper function. 2013-02-15 15:10:37 -05:00
xfrm4_mode_beet.c
xfrm4_mode_transport.c
xfrm4_mode_tunnel.c xfrm: allow to avoid copying DSCP during encapsulation 2013-03-06 07:02:45 +01:00
xfrm4_output.c
xfrm4_policy.c xfrm: make gc_thresh configurable in all namespaces 2013-02-06 11:36:29 +01:00
xfrm4_state.c
xfrm4_tunnel.c sit: add IPv4 over IPv4 support 2013-05-31 17:19:05 -07:00