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f672258391
linux/net/ipv4
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Yuchung Cheng f672258391 tcp: track min RTT using windowed min-filter 
Kathleen Nichols' algorithm for tracking the minimum RTT of a
data stream over some measurement window. It uses constant space
and constant time per update. Yet it almost always delivers
the same minimum as an implementation that has to keep all
the data in the window. The measurement window is tunable via
sysctl.net.ipv4.tcp_min_rtt_wlen with a default value of 5 minutes.

The algorithm keeps track of the best, 2nd best & 3rd best min
values, maintaining an invariant that the measurement time of
the n'th best >= n-1'th best. It also makes sure that the three
values are widely separated in the time window since that bounds
the worse case error when that data is monotonically increasing
over the window.

Upon getting a new min, we can forget everything earlier because
it has no value - the new min is less than everything else in the
window by definition and it's the most recent. So we restart fresh
on every new min and overwrites the 2nd & 3rd choices. The same
property holds for the 2nd & 3rd best.

Therefore we have to maintain two invariants to maximize the
information in the samples, one on values (1st.v <= 2nd.v <=
3rd.v) and the other on times (now-win <=1st.t <= 2nd.t <= 3rd.t <=
now). These invariants determine the structure of the code

The RTT input to the windowed filter is the minimum RTT measured
from ACK or SACK, or as the last resort from TCP timestamps.

The accessor tcp_min_rtt() returns the minimum RTT seen in the
window. ~0U indicates it is not available. The minimum is 1usec
even if the true RTT is below that.

Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
2015-10-21 07:00:43 -07:00
..
netfilter Merge branch 'master' of git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next 2015-10-17 14:28:03 +02:00
af_inet.c net: Replace vrf_dev_table and friends 2015-09-29 20:40:33 -07:00
ah4.c ah4: Fix error return in ah_input(). 2015-08-25 13:38:50 -07:00
arp.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2015-10-20 06:08:27 -07:00
cipso_ipv4.c ipv4: coding style: comparison for inequality with NULL 2015-04-03 12:11:15 -04:00
datagram.c net: Set sk_txhash from a random number 2015-07-29 22:44:04 -07:00
devinet.c rtnetlink: RTEXT_FILTER_SKIP_STATS support to avoid dumping inet/inet6 stats 2015-09-15 15:25:02 -07:00
esp4.c esp4: Switch to new AEAD interface 2015-05-28 11:23:20 +08:00
fib_frontend.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2015-10-02 07:21:25 -07:00
fib_lookup.h ipv4: consider TOS in fib_select_default 2015-07-24 22:46:11 -07:00
fib_rules.c net: ipv6: use common fib_default_rule_pref 2015-09-09 14:19:50 -07:00
fib_semantics.c net: Fix suspicious RCU usage in fib_rebalance 2015-10-16 00:57:55 -07:00
fib_trie.c net: Fix vti use case with oif in dst lookups 2015-09-17 16:36:34 -07:00
fou.c fou: reject IPv6 config 2015-08-29 13:07:54 -07:00
gre_demux.c gre: Remove support for sharing GRE protocol hook. 2015-08-10 14:03:54 -07:00
gre_offload.c ipv4: coding style: comparison for inequality with NULL 2015-04-03 12:11:15 -04:00
icmp.c Revert "ipv4/icmp: redirect messages can use the ingress daddr as source" 2015-10-14 06:01:07 -07:00
igmp.c ipv4, ipv6: Pass net into ip_local_out and ip6_local_out 2015-10-08 04:27:02 -07:00
inet_connection_sock.c tcp/dccp: fix race at listener dismantle phase 2015-10-16 00:52:19 -07:00
inet_diag.c tcp/dccp: install syn_recv requests into ehash table 2015-10-03 04:32:41 -07:00
inet_fragment.c inet: frags: remove INET_FRAG_EVICTED and use list_evictor for the test 2015-07-26 21:00:15 -07:00
inet_hashtables.c tcp/dccp: fix potential NULL deref in __inet_inherit_port() 2015-10-14 19:06:31 -07:00
inet_lro.c
inet_timewait_sock.c tcp/dccp: fix timewait races in timer handling 2015-09-21 16:32:29 -07:00
inetpeer.c net: Add helper function to compare inetpeer addresses 2015-08-28 13:32:36 -07:00
ip_forward.c net: Pass net into dst_output and remove dst_output_okfn 2015-10-08 04:26:54 -07:00
ip_fragment.c ipv4: Pass struct net into ip_defrag and ip_check_defrag 2015-10-12 19:44:16 -07:00
ip_gre.c ip_tunnels: record IP version in tunnel info 2015-08-29 13:07:54 -07:00
ip_input.c ipv4: Pass struct net into ip_defrag and ip_check_defrag 2015-10-12 19:44:16 -07:00
ip_options.c ipv4: coding style: comparison for inequality with NULL 2015-04-03 12:11:15 -04:00
ip_output.c tcp: do not set queue_mapping on SYNACK 2015-10-18 22:26:02 -07:00
ip_sockglue.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2015-06-24 02:58:51 -07:00
ip_tunnel_core.c ipv4, ipv6: Pass net into ip_local_out and ip6_local_out 2015-10-08 04:27:02 -07:00
ip_tunnel.c ip_gre: Add support to collect tunnel metadata. 2015-08-10 14:03:54 -07:00
ip_vti.c net: Pass net into dst_output and remove dst_output_okfn 2015-10-08 04:26:54 -07:00
ipcomp.c ipv4: coding style: comparison for equality with NULL 2015-04-03 12:11:15 -04:00
ipconfig.c ipconfig: send Client-identifier in DHCP requests 2015-10-18 19:23:52 -07:00
ipip.c ip_gre: Add support to collect tunnel metadata. 2015-08-10 14:03:54 -07:00
ipmr.c net: Pass net into dst_output and remove dst_output_okfn 2015-10-08 04:26:54 -07:00
Kconfig geneve: Consolidate Geneve functionality in single module. 2015-08-27 15:42:48 -07:00
Makefile geneve: Consolidate Geneve functionality in single module. 2015-08-27 15:42:48 -07:00
netfilter.c ipv4: Pass struct net into ip_route_me_harder 2015-09-29 20:21:32 +02:00
ping.c ipv6: Nonlocal bind 2015-07-09 21:09:10 -07:00
proc.c net: track success and failure of TCP PMTU probing 2015-07-21 22:36:33 -07:00
protocol.c net: Export inet_offloads and inet6_offloads 2014-09-19 17:15:31 -04:00
raw.c net: Pass net into dst_output and remove dst_output_okfn 2015-10-08 04:26:54 -07:00
route.c net: Do not drop to make_route if oif is l3mdev 2015-10-08 05:18:47 -07:00
syncookies.c net: shrink struct sock and request_sock by 8 bytes 2015-10-12 19:28:22 -07:00
sysctl_net_ipv4.c tcp: track min RTT using windowed min-filter 2015-10-21 07:00:43 -07:00
tcp_bic.c tcp: add tcp_in_slow_start helper 2015-07-09 14:22:52 -07:00
tcp_cdg.c tcp: do not slow start when cwnd equals ssthresh 2015-07-09 14:22:52 -07:00
tcp_cong.c tcp: remove tcp_ecn_make_synack() socket argument 2015-09-25 13:00:38 -07:00
tcp_cubic.c tcp_cubic: do not set epoch_start in the future 2015-09-17 22:35:07 -07:00
tcp_dctcp.c net: tcp: dctcp_update_alpha() fixes. 2015-06-10 23:28:33 -07:00
tcp_diag.c sock_diag: implement a get_info handler for inet 2015-06-15 19:49:22 -07:00
tcp_fastopen.c tcp: fix fastopen races vs lockless listener 2015-10-05 02:45:24 -07:00
tcp_highspeed.c tcp: add tcp_in_slow_start helper 2015-07-09 14:22:52 -07:00
tcp_htcp.c tcp: add tcp_in_slow_start helper 2015-07-09 14:22:52 -07:00
tcp_hybla.c tcp: do not slow start when cwnd equals ssthresh 2015-07-09 14:22:52 -07:00
tcp_illinois.c tcp: add tcp_in_slow_start helper 2015-07-09 14:22:52 -07:00
tcp_input.c tcp: track min RTT using windowed min-filter 2015-10-21 07:00:43 -07:00
tcp_ipv4.c tcp: do not set queue_mapping on SYNACK 2015-10-18 22:26:02 -07:00
tcp_lp.c tcp: remove in_flight parameter from cong_avoid() methods 2014-05-03 19:23:07 -04:00
tcp_memcontrol.c memcg: cleanup static keys decrement 2015-02-12 18:54:10 -08:00
tcp_metrics.c net: Add helper function to compare inetpeer addresses 2015-08-28 13:32:36 -07:00
tcp_minisocks.c tcp: track min RTT using windowed min-filter 2015-10-21 07:00:43 -07:00
tcp_offload.c tcp: reserve tcp_skb_mss() to tcp stack 2015-06-11 16:33:10 -07:00
tcp_output.c tcp: do not set queue_mapping on SYNACK 2015-10-18 22:26:02 -07:00
tcp_probe.c tcp: whitespace fixes 2014-09-01 18:12:45 -07:00
tcp_scalable.c tcp: add tcp_in_slow_start helper 2015-07-09 14:22:52 -07:00
tcp_timer.c tcp: change type of alive from int to bool 2015-10-12 05:15:03 -07:00
tcp_vegas.c tcp: add tcp_in_slow_start helper 2015-07-09 14:22:52 -07:00
tcp_vegas.h tcp: prepare CC get_info() access from getsockopt() 2015-04-29 17:10:38 -04:00
tcp_veno.c tcp: add tcp_in_slow_start helper 2015-07-09 14:22:52 -07:00
tcp_westwood.c tcp_westwood: fix tcp_westwood_info() 2015-05-05 19:50:09 -04:00
tcp_yeah.c tcp: stretch ACK fixes prep 2015-01-28 22:18:37 -08:00
tcp.c tcp: track min RTT using windowed min-filter 2015-10-21 07:00:43 -07:00
tunnel4.c
udp_diag.c sock_diag: specify info_size per inet protocol 2015-06-15 19:49:22 -07:00
udp_impl.h net: Remove iocb argument from sendmsg and recvmsg 2015-03-02 13:06:31 -05:00
udp_offload.c ipv4: coding style: comparison for inequality with NULL 2015-04-03 12:11:15 -04:00
udp_tunnel.c tunnel: introduce udp_tun_rx_dst() 2015-08-27 15:42:47 -07:00
udp.c net: SO_INCOMING_CPU setsockopt() support 2015-10-12 19:28:20 -07:00
udplite.c net: Eliminate no_check from protosw 2014-05-23 16:28:53 -04:00
xfrm4_input.c netfilter: Pass net into okfn 2015-09-17 17:18:37 -07:00
xfrm4_mode_beet.c
xfrm4_mode_transport.c
xfrm4_mode_tunnel.c ipv4: hash net ptr into fragmentation bucket selection 2015-03-25 14:07:04 -04:00
xfrm4_output.c dst: Pass net into dst->output 2015-10-08 04:27:03 -07:00
xfrm4_policy.c ipv4: Merge __ip_local_out and __ip_local_out_sk 2015-10-08 04:26:57 -07:00
xfrm4_protocol.c xfrm4: Remove duplicate semicolon 2014-06-30 07:49:47 +02:00
xfrm4_state.c
xfrm4_tunnel.c