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Jianfeng Wang fb264505b3 tcp: apply a floor of 1 for RTT samples from TCP timestamps 
[ Upstream commit 730e700e2c ]

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
 		2020-08-11 15:33:41 +02:00
..
bpfilter SPDX update for 5.2-rc2, round 1 2019-05-21 12:33:38 -07:00
netfilter netfilter: nf_conntrack_pptp: prevent buffer overflows in debug code 2020-06-03 08:21:35 +02:00
Kconfig vti[6]: fix packet tx through bpf_redirect() in XinY cases 2020-04-01 11:02:05 +02:00
Makefile net: Initial nexthop code 2019-05-28 21:37:30 -07:00
af_inet.c net: remove empty inet_exit_net 2019-08-19 18:22:54 -07:00
ah4.c xfrm: remove type and offload_type map from xfrm_state_afinfo 2019-06-06 08:34:50 +02:00
arp.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
cipso_ipv4.c netlabel: cope with NULL catmap 2020-05-20 08:20:08 +02:00
datagram.c inet: stop leaking jiffies on the wire 2019-11-01 14:57:52 -07:00
devinet.c devinet: fix memleak in inetdev_init() 2020-06-10 20:24:54 +02:00
esp4.c xfrm: remove get_mtu indirection from xfrm_type 2019-07-01 06:16:40 +02:00
esp4_offload.c xfrm: remove the xfrm_state_put call becofe going to out_reset 2020-06-03 08:21:32 +02:00
fib_frontend.c ipv4: nexthop version of fib_info_nh_uses_dev 2020-06-03 08:21:37 +02:00
fib_lookup.h ipv4: Use accessors for fib_info nexthop data 2019-06-04 19:26:49 -07:00
fib_notifier.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
fib_rules.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2019-06-07 11:00:14 -07:00
fib_semantics.c net: Fix the arp error in some cases 2020-06-30 15:36:44 -04:00
fib_trie.c ipv4: Silence suspicious RCU usage warning 2020-08-11 15:33:39 +02:00
fou.c fou: Fix IPv6 netlink policy 2020-01-29 16:45:22 +01:00
gre_demux.c gre: fix uninit-value in __iptunnel_pull_header 2020-03-18 07:17:38 +01:00
gre_offload.c net: gre: recompute gre csum for sctp over gre tunnels 2020-08-11 15:33:40 +02:00
icmp.c ip: Fix SO_MARK in RST, ACK and ICMP packets 2020-07-22 09:32:50 +02:00
igmp.c net: fix __ip_mc_inc_group usage 2019-08-20 12:48:06 -07:00
inet_connection_sock.c net: inet_csk: Fix so_reuseport bind-address cache in tb->fast* 2020-06-03 08:20:48 +02:00
inet_diag.c inet_diag: return classid for all socket types 2020-03-18 07:17:38 +01:00
inet_fragment.c inet: frags: re-introduce skb coalescing for local delivery 2019-08-08 15:55:10 -07:00
inet_hashtables.c tcp/dccp: fix possible race __inet_lookup_established() 2020-01-04 19:19:13 +01:00
inet_timewait_sock.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
inetpeer.c inetpeer: fix data-race in inet_putpeer / inet_putpeer 2020-01-04 19:18:39 +01:00
ip_forward.c ipv4: Revert removal of rt_uses_gateway 2019-09-20 18:23:33 -07:00
ip_fragment.c inet: frags: re-introduce skb coalescing for local delivery 2019-08-08 15:55:10 -07:00
ip_gre.c net: ip_gre: Accept IFLA_INFO_DATA-less configuration 2020-04-01 11:01:46 +02:00
ip_input.c netfilter: drop bridge nf reset from nf_reset 2019-10-01 18:42:15 +02:00
ip_options.c netfilter: nf_tables: add support for matching IPv4 options 2019-06-21 18:35:51 +02:00
ip_output.c ip: Fix SO_MARK in RST, ACK and ICMP packets 2020-07-22 09:32:50 +02:00
ip_sockglue.c ip_sockglue: Fix missing-check bug in ip_ra_control() 2019-05-25 11:00:50 -07:00
ip_tunnel.c ip_tunnel: fix use-after-free in ip_tunnel_lookup() 2020-06-30 15:36:46 -04:00
ip_tunnel_core.c ip_tunnel: allow not to count pkts on tstats by setting skb's dev to NULL 2019-06-18 20:48:45 -04:00
ip_vti.c ip_vti: receive ipip packet by calling ip_tunnel_rcv 2020-06-03 08:21:34 +02:00
ipcomp.c Merge branch 'master' of git://git.kernel.org/pub/scm/linux/kernel/git/klassert/ipsec-next 2019-07-05 15:01:15 -07:00
ipconfig.c ipconfig: add carrier_timeout kernel parameter 2019-02-01 15:24:13 -08:00
ipip.c net: ipip: fix wrong address family in init error path 2020-06-03 08:20:52 +02:00
ipmr.c net: don't return invalid table id error when we fall back to PF_UNSPEC 2020-06-03 08:20:41 +02:00
ipmr_base.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2019-05-07 17:22:09 -07:00
metrics.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
netfilter.c netfilter: ipv4: remove useless export_symbol 2019-01-28 11:32:58 +01:00
netlink.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
nexthop.c nexthops: don't modify published nexthop groups 2020-06-03 08:21:37 +02:00
ping.c ipv4: fill fl4_icmp_{type,code} in ping_v4_sendmsg 2020-07-22 09:32:47 +02:00
proc.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2019-06-17 20:20:36 -07:00
protocol.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
raw.c netfilter: drop bridge nf reset from nf_reset 2019-10-01 18:42:15 +02:00
raw_diag.c inet_diag: return classid for all socket types 2020-03-18 07:17:38 +01:00
route.c net: revert "net: get rid of an signed integer overflow in ip_idents_reserve()" 2020-06-03 08:21:00 +02:00
syncookies.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
sysctl_net_ipv4.c net/ipv4: fix sysctl max for fib_multipath_hash_policy 2019-11-18 17:25:36 -08:00
tcp.c tcp: md5: allow changing MD5 keys in all socket states 2020-07-22 09:32:49 +02:00
tcp_bbr.c tcp_bbr: improve arithmetic division in bbr_update_bw() 2020-01-29 16:45:21 +01:00
tcp_bic.c treewide: Add SPDX license identifier for more missed files 2019-05-21 10:50:45 +02:00
tcp_bpf.c bpf/sockmap: Fix kernel panic at __tcp_bpf_recvmsg 2020-06-24 17:50:42 +02:00
tcp_cdg.c treewide: Add SPDX license identifier for more missed files 2019-05-21 10:50:45 +02:00
tcp_cong.c tcp: make sure listeners don't initialize congestion-control state 2020-07-22 09:32:48 +02:00
tcp_cubic.c tcp_cubic: fix spurious HYSTART_DELAY exit upon drop in min RTT 2020-06-30 15:36:47 -04:00
tcp_dctcp.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
tcp_dctcp.h tcp: refactor DCTCP ECN ACK handling 2018-10-10 22:26:00 -07:00
tcp_diag.c tcp: annotate tp->write_seq lockless reads 2019-10-13 10:13:08 -07:00
tcp_fastopen.c tcp: add rcu protection around tp->fastopen_rsk 2019-10-13 10:13:08 -07:00
tcp_highspeed.c treewide: Add SPDX license identifier for more missed files 2019-05-21 10:50:45 +02:00
tcp_htcp.c treewide: Add SPDX license identifier for more missed files 2019-05-21 10:50:45 +02:00
tcp_hybla.c treewide: Add SPDX license identifier for more missed files 2019-05-21 10:50:45 +02:00
tcp_illinois.c treewide: Add SPDX license identifier for more missed files 2019-05-21 10:50:45 +02:00
tcp_input.c tcp: apply a floor of 1 for RTT samples from TCP timestamps 2020-08-11 15:33:41 +02:00
tcp_ipv4.c tcp: md5: refine tcp_md5_do_add()/tcp_md5_hash_key() barriers 2020-07-22 09:32:49 +02:00
tcp_lp.c treewide: Add SPDX license identifier for more missed files 2019-05-21 10:50:45 +02:00
tcp_metrics.c tcp: refactor setting the initial congestion window 2019-05-01 11:47:54 -04:00
tcp_minisocks.c tcp: annotate tp->snd_nxt lockless reads 2019-10-13 10:13:08 -07:00
tcp_nv.c treewide: Add SPDX license identifier for more missed files 2019-05-21 10:50:45 +02:00
tcp_offload.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
tcp_output.c tcp: allow at most one TLP probe per flight 2020-07-31 18:39:31 +02:00
tcp_rate.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
tcp_recovery.c tcp: introduce tcp_skb_timestamp_us() helper 2018-09-21 19:37:59 -07:00
tcp_scalable.c treewide: Add SPDX license identifier for more missed files 2019-05-21 10:50:45 +02:00
tcp_timer.c tcp: add rcu protection around tp->fastopen_rsk 2019-10-13 10:13:08 -07:00
tcp_ulp.c bpf: Sockmap/tls, push write_space updates through ulp updates 2020-01-23 08:22:45 +01:00
tcp_vegas.c treewide: Add SPDX license identifier for more missed files 2019-05-21 10:50:45 +02:00
tcp_vegas.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
tcp_veno.c treewide: Add SPDX license identifier for more missed files 2019-05-21 10:50:45 +02:00
tcp_westwood.c treewide: Add SPDX license identifier for more missed files 2019-05-21 10:50:45 +02:00
tcp_yeah.c treewide: Add SPDX license identifier for more missed files 2019-05-21 10:50:45 +02:00
tunnel4.c treewide: Add SPDX license identifier for more missed files 2019-05-21 10:50:45 +02:00
udp.c udp: Improve load balancing for SO_REUSEPORT. 2020-07-31 18:39:31 +02:00
udp_diag.c inet_diag: return classid for all socket types 2020-03-18 07:17:38 +01:00
udp_impl.h udp: add missing rehash callback to udplite 2019-01-17 15:01:08 -08:00
udp_offload.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2019-06-22 08:59:24 -04:00
udp_tunnel.c treewide: Add SPDX license identifier for more missed files 2019-05-21 10:50:45 +02:00
udplite.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
xfrm4_input.c xfrm: reset transport header back to network header after all input transforms ahave been applied 2018-09-04 10:26:30 +02:00
xfrm4_output.c xfrm: Always set XFRM_TRANSFORMED in xfrm{4,6}_output_finish 2020-04-29 16:33:11 +02:00
xfrm4_policy.c net: add bool confirm_neigh parameter for dst_ops.update_pmtu 2020-01-04 19:18:58 +01:00
xfrm4_protocol.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152 2019-05-30 11:26:32 -07:00
xfrm4_state.c xfrm: remove eth_proto value from xfrm_state_afinfo 2019-06-06 08:34:50 +02:00
xfrm4_tunnel.c xfrm: remove type and offload_type map from xfrm_state_afinfo 2019-06-06 08:34:50 +02:00