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4a5ab4e224
linux/net/ipv4
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Eric Dumazet 4a5ab4e224 tcp: remove 1ms offset in srtt computation 
TCP pacing depends on an accurate srtt estimation.

Current srtt estimation is using jiffie resolution,
and has an artificial offset of at least 1 ms, which can produce
slowdowns when FQ/pacing is used, especially in DC world,
where typical rtt is below 1 ms.

We are planning a switch to usec resolution for linux-3.15,
but in the meantime, this patch removes the 1 ms offset.

All we need is to have tp->srtt minimal value of 1 to differentiate
the case of srtt being initialized or not, not 8.

The problematic behavior was observed on a 40Gbit testbed,
where 32 concurrent netperf were reaching 12Gbps of aggregate
speed, instead of line speed.

This patch also has the effect of reporting more accurate srtt and send
rates to iproute2 ss command as in :

$ ss -i dst cca2
Netid  State      Recv-Q Send-Q          Local Address:Port
Peer Address:Port
tcp    ESTAB      0      0                10.244.129.1:56984
10.244.129.2:12865
	 cubic wscale:6,6 rto:200 rtt:0.25/0.25 ato:40 mss:1448 cwnd:10 send
463.4Mbps rcv_rtt:1 rcv_space:29200
tcp    ESTAB      0      390960           10.244.129.1:60247
10.244.129.2:50204
	 cubic wscale:6,6 rto:200 rtt:0.875/0.75 mss:1448 cwnd:73 ssthresh:51
send 966.4Mbps unacked:73 retrans:0/121 rcv_space:29200

Reported-by: Vytautas Valancius <valas@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
2014-02-06 21:28:06 -08:00
..
netfilter netfilter: nf_tables: fix error path in the init functions 2014-01-09 23:25:48 +01:00
af_inet.c ipv4: introduce hardened ip_no_pmtu_disc mode 2014-01-13 11:22:55 -08:00
ah4.c ipv4: properly refresh rtable entries on pmtu/redirect events 2013-06-03 00:07:42 -07:00
arp.c ipv4: arp: update neighbour address when a gratuitous arp is received and arp_accept is set 2014-01-02 00:08:38 -05:00
cipso_ipv4.c ipv4: ERROR: code indent should use tabs where possible 2013-12-26 13:43:21 -05:00
datagram.c net: Remove FLOWI_FLAG_CAN_SLEEP 2013-12-06 07:24:39 +01:00
devinet.c ipv4: Fix runtime WARNING in rtmsg_ifa() 2014-02-06 20:02:15 -08:00
esp4.c net: esp{4,6}: get rid of struct esp_data 2013-10-29 06:39:42 +01:00
fib_frontend.c fib_frontend: fix possible NULL pointer dereference 2014-01-24 15:51:26 -08:00
fib_lookup.h ipv4: make fib_detect_death static 2013-12-28 17:01:46 -05:00
fib_rules.c inet: fix NULL pointer Oops in fib(6)_rule_suppress 2013-12-10 17:54:23 -05:00
fib_semantics.c ipv4: make fib_detect_death static 2013-12-28 17:01:46 -05:00
fib_trie.c seq_file: remove "%n" usage from seq_file users 2013-11-15 09:32:20 +09:00
gre_demux.c gre_offload: statically build GRE offloading support 2014-01-06 20:28:34 -05:00
gre_offload.c net/ipv4: don't use module_init in non-modular gre_offload 2014-01-16 16:08:27 -08:00
icmp.c ipv4: introduce hardened ip_no_pmtu_disc mode 2014-01-13 11:22:55 -08:00
igmp.c net: replace macros net_random and net_srandom with direct calls to prandom 2014-01-14 15:15:25 -08:00
inet_connection_sock.c net: replace macros net_random and net_srandom with direct calls to prandom 2014-01-14 15:15:25 -08:00
inet_diag.c inet_diag: fix inet_diag_dump_icsk() to use correct state for timewait sockets 2014-01-13 22:35:46 -08:00
inet_fragment.c inet: remove old fragmentation hash initializing 2013-10-23 17:01:41 -04:00
inet_hashtables.c inet: convert inet_ehash_secret and ipv6_hash_secret to net_get_random_once 2013-10-19 19:45:35 -04:00
inet_lro.c lro: remove dead code 2013-12-29 16:34:25 -05:00
inet_timewait_sock.c tcp/dccp: remove twchain 2013-10-08 23:19:24 -04:00
inetpeer.c ipv4: remove unused function 2013-12-28 17:03:20 -05:00
ip_forward.c ipv4: introduce ip_dst_mtu_maybe_forward and protect forwarding path against pmtu spoofing 2014-01-13 11:22:54 -08:00
ip_fragment.c net: Add utility functions to clear rxhash 2013-12-17 16:36:21 -05:00
ip_gre.c net: gre: use icmp_hdr() to get inner ip header 2014-01-27 20:38:26 -08:00
ip_input.c net: Fix memory leak if TPROXY used with TCP early demux 2014-01-27 16:22:11 -08:00
ip_options.c ipv4: switch and case should be at the same indent 2014-01-02 03:30:36 -05:00
ip_output.c ipv4: register igmp_notifier even when !CONFIG_PROC_FS 2014-01-14 15:03:33 -08:00
ip_sockglue.c ipv6: make IPV6_RECVPKTINFO work for ipv4 datagrams 2014-01-19 19:53:18 -08:00
ip_tunnel_core.c net: Add utility functions to clear rxhash 2013-12-17 16:36:21 -05:00
ip_tunnel.c ip_tunnel: fix panic in ip_tunnel_xmit() 2014-02-03 13:01:48 -08:00
ip_vti.c ipv4: be friend with drop monitor 2014-01-18 23:08:02 -08:00
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 ipv4: be friend with drop monitor 2014-01-18 23:08:02 -08:00
ipmr.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2014-01-18 00:55:41 -08:00
Kconfig net: neighbour: Remove CONFIG_ARPD 2013-09-03 21:41:43 -04:00
Makefile gre_offload: statically build GRE offloading support 2014-01-06 20:28:34 -05:00
netfilter.c netfilter: add my copyright statements 2013-04-18 20:27:55 +02:00
ping.c ipv6: protect protocols not handling ipv4 from v4 connection/bind attempts 2014-01-21 16:59:19 -08:00
proc.c ipv4: spaces required around that '=' 2014-01-02 03:30:36 -05:00
protocol.c net: remove outdated comment for ipv4 and ipv6 protocol handler 2013-11-28 18:47:51 -05:00
raw.c net: add build-time checks for msg->msg_name size 2014-01-18 23:04:16 -08:00
route.c ipv4: introduce ip_dst_mtu_maybe_forward and protect forwarding path against pmtu spoofing 2014-01-13 11:22:54 -08:00
syncookies.c ipv4: fix checkpatch error "space prohibited" 2013-12-26 13:43:21 -05:00
sysctl_net_ipv4.c ipv4: introduce ip_dst_mtu_maybe_forward and protect forwarding path against pmtu spoofing 2014-01-13 11:22:54 -08:00
tcp_bic.c tcp: properly handle stretch acks in slow start 2013-11-04 19:57:59 -05:00
tcp_cong.c tcp: properly handle stretch acks in slow start 2013-11-04 19:57:59 -05:00
tcp_cubic.c tcp: properly handle stretch acks in slow start 2013-11-04 19:57:59 -05:00
tcp_diag.c
tcp_fastopen.c tcp: enable sockets to use MSG_FASTOPEN by default 2013-11-04 19:57:47 -05:00
tcp_highspeed.c tcp: properly handle stretch acks in slow start 2013-11-04 19:57:59 -05:00
tcp_htcp.c tcp: properly handle stretch acks in slow start 2013-11-04 19:57:59 -05:00
tcp_hybla.c tcp: properly handle stretch acks in slow start 2013-11-04 19:57:59 -05:00
tcp_illinois.c remove extra definitions of U32_MAX 2014-01-23 16:36:55 -08:00
tcp_input.c tcp: remove 1ms offset in srtt computation 2014-02-06 21:28:06 -08:00
tcp_ipv4.c tcp: delete redundant calls of tcp_mtup_init() 2014-01-21 16:52:31 -08:00
tcp_lp.c tcp: properly handle stretch acks in slow start 2013-11-04 19:57:59 -05:00
tcp_memcontrol.c tcp_memcontrol: Cleanup/fix cg_proto->memory_pressure handling. 2013-12-05 21:01:01 -05:00
tcp_metrics.c tcp: metrics: Handle v6/v4-mapped sockets in tcp-metrics 2014-01-23 12:48:28 -08:00
tcp_minisocks.c ipv6: tcp: fix flowlabel value in ACK messages send from TIME_WAIT 2014-01-17 17:56:33 -08:00
tcp_offload.c tcp: do not export tcp_gso_segment() and tcp_gro_receive() 2014-01-14 18:53:48 -08:00
tcp_output.c tcp: remove 1ms offset in srtt computation 2014-02-06 21:28:06 -08:00
tcp_probe.c ipv4: ERROR: do not initialise globals to 0 or NULL 2013-12-26 13:43:21 -05:00
tcp_scalable.c tcp: properly handle stretch acks in slow start 2013-11-04 19:57:59 -05:00
tcp_timer.c tcp: temporarily disable Fast Open on SYN timeout 2013-10-29 22:50:41 -04:00
tcp_vegas.c tcp: properly handle stretch acks in slow start 2013-11-04 19:57:59 -05:00
tcp_vegas.h net: ipv4/ipv6: Remove extern from function prototypes 2013-10-19 19:12:11 -04:00
tcp_veno.c tcp: properly handle stretch acks in slow start 2013-11-04 19:57:59 -05:00
tcp_westwood.c tcp: refactor F-RTO 2013-03-21 11:47:50 -04:00
tcp_yeah.c ipv4: ipv4: Cleanup the comments in tcp_yeah.c 2013-12-26 13:43:55 -05:00
tcp.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next 2014-01-25 11:17:34 -08:00
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 net: ipv4/ipv6: Remove extern from function prototypes 2013-10-19 19:12:11 -04:00
udp_offload.c net/ipv4: Use proper RCU APIs for writer-side in udp_offload.c 2014-02-04 20:01:55 -08:00
udp.c net: add build-time checks for msg->msg_name size 2014-01-18 23:04:16 -08:00
udplite.c net: ipv4: Standardize prefixes for message logging 2012-03-12 17:05:21 -07:00
xfrm4_input.c net: Add skb_unclone() helper function. 2013-02-15 15:10:37 -05:00
xfrm4_mode_beet.c ipv4: ERROR: code indent should use tabs where possible 2013-12-26 13:43:21 -05:00
xfrm4_mode_transport.c
xfrm4_mode_tunnel.c Merge branch 'master' of git://git.kernel.org/pub/scm/linux/kernel/git/klassert/ipsec-next 2013-09-30 15:24:57 -04:00
xfrm4_output.c xfrm: revert ipv4 mtu determination to dst_mtu 2013-08-26 12:40:53 +02:00
xfrm4_policy.c xfrm: Fix null pointer dereference when decoding sessions 2013-11-01 07:08:46 +01:00
xfrm4_state.c inet: make no_pmtu_disc per namespace and kill ipv4_config 2013-12-18 16:58:20 -05:00
xfrm4_tunnel.c sit: add IPv4 over IPv4 support 2013-05-31 17:19:05 -07:00