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190f8b060e
linux/net/ipv4
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Jianfeng Wang 730e700e2c tcp: apply a floor of 1 for RTT samples from TCP timestamps 
For retransmitted packets, TCP needs to resort to using TCP timestamps
for computing RTT samples. In the common case where the data and ACK
fall in the same 1-millisecond interval, TCP senders with millisecond-
granularity TCP timestamps compute a ca_rtt_us of 0. This ca_rtt_us
of 0 propagates to rs->rtt_us.

This value of 0 can cause performance problems for congestion control
modules. For example, in BBR, the zero min_rtt sample can bring the
min_rtt and BDP estimate down to 0, reduce snd_cwnd and result in a
low throughput. It would be hard to mitigate this with filtering in
the congestion control module, because the proper floor to apply would
depend on the method of RTT sampling (using timestamp options or
internally-saved transmission timestamps).

This fix applies a floor of 1 for the RTT sample delta from TCP
timestamps, so that seq_rtt_us, ca_rtt_us, and rs->rtt_us will be at
least 1 * (USEC_PER_SEC / TCP_TS_HZ).

Note that the receiver RTT computation in tcp_rcv_rtt_measure() and
min_rtt computation in tcp_update_rtt_min() both already apply a floor
of 1 timestamp tick, so this commit makes the code more consistent in
avoiding this edge case of a value of 0.

Signed-off-by: Jianfeng Wang <jfwang@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Kevin Yang <yyd@google.com>
Acked-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
2020-08-03 17:54:03 -07:00
..
bpfilter net: improve the user pointer check in init_user_sockptr 2020-07-28 13:43:40 -07:00
netfilter net: remove sockptr_advance 2020-07-28 13:43:40 -07:00
af_inet.c net: remove compat_sock_common_{get,set}sockopt 2020-07-19 18:16:40 -07:00
ah4.c inet: Use fallthrough; 2020-03-12 15:55:00 -07:00
arp.c inet: Use fallthrough; 2020-03-12 15:55:00 -07:00
bpf_tcp_ca.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next 2020-03-30 19:52:37 -07:00
cipso_ipv4.c net: ipv4: kerneldoc fixes 2020-07-13 17:20:39 -07:00
datagram.c
devinet.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2020-05-31 17:48:46 -07:00
esp4_offload.c net: Add MODULE_DESCRIPTION entries to network modules 2020-06-20 21:33:57 -07:00
esp4.c ESP: Export esp_output_fill_trailer function 2020-02-19 13:52:32 +01:00
fib_frontend.c ipv4: nexthop version of fib_info_nh_uses_dev 2020-05-26 16:06:07 -07:00
fib_lookup.h net: add net available in build_state 2020-03-29 22:30:57 -07:00
fib_notifier.c
fib_rules.c fib: use indirect call wrappers in the most common fib_rules_ops 2020-07-28 17:42:31 -07:00
fib_semantics.c net: Fix the arp error in some cases 2020-06-18 20:21:51 -07:00
fib_trie.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2020-08-02 01:02:12 -07:00
fou.c net: Add MODULE_DESCRIPTION entries to network modules 2020-06-20 21:33:57 -07:00
gre_demux.c gre: fix uninit-value in __iptunnel_pull_header 2020-03-08 21:25:37 -07:00
gre_offload.c net: gre: recompute gre csum for sctp over gre tunnels 2020-08-03 15:29:44 -07:00
icmp.c icmp6: support rfc 4884 2020-07-24 17:12:41 -07:00
igmp.c ip*_mc_gsfget(): lift copyout of struct group_filter into callers 2020-05-20 20:31:27 -04:00
inet_connection_sock.c net/ipv6: remove compat_ipv6_{get,set}sockopt 2020-07-19 18:16:41 -07:00
inet_diag.c inet_diag: support for wider protocol numbers 2020-07-09 12:38:41 -07:00
inet_fragment.c
inet_hashtables.c inet: Run SK_LOOKUP BPF program on socket lookup 2020-07-17 20:18:16 -07:00
inet_timewait_sock.c
inetpeer.c
ip_forward.c
ip_fragment.c
ip_gre.c net: add a new ndo_tunnel_ioctl method 2020-05-19 15:45:11 -07:00
ip_input.c bpf: Add socket assign support 2020-03-30 13:45:04 -07:00
ip_options.c net/ipv4: merge ip_options_get and ip_options_get_from_user 2020-07-24 15:41:54 -07:00
ip_output.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2020-07-11 00:46:00 -07:00
ip_sockglue.c icmp: prepare rfc 4884 for ipv6 2020-07-24 17:12:41 -07:00
ip_tunnel_core.c net: ip_tunnel: add header_ops for layer 3 devices 2020-06-30 12:29:39 -07:00
ip_tunnel.c ip_tunnel: fix use-after-free in ip_tunnel_lookup() 2020-06-18 20:12:34 -07:00
ip_vti.c Merge branch 'master' of git://git.kernel.org/pub/scm/linux/kernel/git/klassert/ipsec-next 2020-07-30 14:39:31 -07:00
ipcomp.c ipcomp: assign if_id to child tunnel from parent tunnel 2020-07-09 12:55:37 +02:00
ipconfig.c Documentation: nfsroot.rst: Fix references to nfsroot.rst 2020-03-02 13:11:46 -07:00
ipip.c net: ipip: implement header_ops->parse_protocol for AF_PACKET 2020-06-30 12:29:39 -07:00
ipmr_base.c
ipmr.c ipmr: Copy option to correct variable 2020-07-27 11:39:55 -07:00
Kconfig Replace HTTP links with HTTPS ones: IPv* 2020-07-06 13:23:03 -07:00
Makefile udp_tunnel: add central NIC RX port offload infrastructure 2020-07-10 13:54:00 -07:00
metrics.c
netfilter.c
netlink.c
nexthop.c nexthop: Fix fdb labeling for groups 2020-06-10 13:18:40 -07:00
ping.c ipv4: fill fl4_icmp_{type,code} in ping_v4_sendmsg 2020-07-07 15:26:37 -07:00
proc.c tcp: add SNMP counter for no. of duplicate segments reported by DSACK 2020-07-17 12:54:30 -07:00
protocol.c
raw_diag.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2020-03-12 22:34:48 -07:00
raw.c net: pass a sockptr_t into ->setsockopt 2020-07-24 15:41:54 -07:00
route.c net: ipv4: Fix wrong type conversion from hint to rt in ip_route_use_hint() 2020-06-27 18:02:32 -07:00
syncookies.c tcp: fix build fong CONFIG_MPTCP=n 2020-08-01 11:46:29 -07:00
sysctl_net_ipv4.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next 2020-05-01 17:02:27 -07:00
tcp_bbr.c
tcp_bic.c tcp: fix stretch ACK bugs in BIC 2020-03-16 18:26:54 -07:00
tcp_bpf.c bpf: tcp: Recv() should return 0 when the peer socket is closed 2020-06-12 15:10:12 -07:00
tcp_cdg.c
tcp_cong.c tcp: make sure listeners don't initialize congestion-control state 2020-07-09 13:07:45 -07:00
tcp_cubic.c tcp_cubic: fix spurious HYSTART_DELAY exit upon drop in min RTT 2020-06-25 16:08:47 -07:00
tcp_dctcp.c
tcp_dctcp.h
tcp_diag.c inet_diag: Move the INET_DIAG_REQ_BYTECODE nlattr to cb->data 2020-02-27 18:50:19 -08:00
tcp_fastopen.c
tcp_highspeed.c Replace HTTP links with HTTPS ones: IPv* 2020-07-06 13:23:03 -07:00
tcp_htcp.c Replace HTTP links with HTTPS ones: IPv* 2020-07-06 13:23:03 -07:00
tcp_hybla.c
tcp_illinois.c
tcp_input.c tcp: apply a floor of 1 for RTT samples from TCP timestamps 2020-08-03 17:54:03 -07:00
tcp_ipv4.c net/tcp: switch ->md5_parse to sockptr_t 2020-07-24 15:41:54 -07:00
tcp_lp.c
tcp_metrics.c
tcp_minisocks.c mptcp: add new sock flag to deal with join subflows 2020-05-15 12:30:13 -07:00
tcp_nv.c
tcp_offload.c
tcp_output.c tcp: rename request_sock cookie_ts bit to syncookie 2020-07-31 16:55:32 -07:00
tcp_rate.c
tcp_recovery.c
tcp_scalable.c tcp: fix stretch ACK bugs in Scalable 2020-03-16 18:26:54 -07:00
tcp_timer.c net: ipv4: kerneldoc fixes 2020-07-13 17:20:39 -07:00
tcp_ulp.c bpf: sockmap: Only check ULP for TCP sockets 2020-03-09 22:34:58 +01:00
tcp_vegas.c
tcp_vegas.h
tcp_veno.c Replace HTTP links with HTTPS ones: IPv* 2020-07-06 13:23:03 -07:00
tcp_westwood.c
tcp_yeah.c tcp: fix stretch ACK bugs in Yeah 2020-03-16 18:26:55 -07:00
tcp.c tcp: add earliest departure time to SCM_TIMESTAMPING_OPT_STATS 2020-07-31 17:00:44 -07:00
tunnel4.c tunnel4: add cb_handler to struct xfrm_tunnel 2020-07-09 12:51:36 +02:00
udp_bpf.c bpf: Add sockmap hooks for UDP sockets 2020-03-09 22:34:58 +01:00
udp_diag.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2020-03-12 22:34:48 -07:00
udp_impl.h net: pass a sockptr_t into ->setsockopt 2020-07-24 15:41:54 -07:00
udp_offload.c udp: initialize is_flist with 0 in udp_gro_receive 2020-03-30 10:35:03 -07:00
udp_tunnel_core.c udp_tunnel: add central NIC RX port offload infrastructure 2020-07-10 13:54:00 -07:00
udp_tunnel_nic.c ethtool: add tunnel info interface 2020-07-10 13:54:00 -07:00
udp_tunnel_stub.c udp_tunnel: add central NIC RX port offload infrastructure 2020-07-10 13:54:00 -07:00
udp.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2020-07-25 17:49:04 -07:00
udplite.c net/ipv4: remove compat_ip_{get,set}sockopt 2020-07-19 18:16:41 -07:00
xfrm4_input.c xfrm: state: remove extract_input indirection from xfrm_state_afinfo 2020-05-06 09:40:08 +02:00
xfrm4_output.c xfrm: fix unused variable warning if CONFIG_NETFILTER=n 2020-05-11 15:12:27 +02:00
xfrm4_policy.c
xfrm4_protocol.c
xfrm4_state.c xfrm: remove output_finish indirection from xfrm_state_afinfo 2020-05-06 09:40:08 +02:00
xfrm4_tunnel.c