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| author | Eric Dumazet <edumazet@google.com> | 2014-02-26 14:02:48 -0800 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2014-02-26 17:08:40 -0500 |
| commit | 740b0f1841f6e39085b711d41db9ffb07198682b (patch) | |
| tree | 7befd549fc20c51bff4c79790ad4520fcc0e324e /include/linux/tcp.h | |
| parent | 363ec392352e55c61ce2799c3f15f89f9429bba7 (diff) | |
| download | lwn-740b0f1841f6e39085b711d41db9ffb07198682b.tar.gz lwn-740b0f1841f6e39085b711d41db9ffb07198682b.zip | |
tcp: switch rtt estimations to usec resolution
Upcoming congestion controls for TCP require usec resolution for RTT
estimations. Millisecond resolution is simply not enough these days.
FQ/pacing in DC environments also require this change for finer control
and removal of bimodal behavior due to the current hack in
tcp_update_pacing_rate() for 'small rtt'
TCP_CONG_RTT_STAMP is no longer needed.
As Julian Anastasov pointed out, we need to keep user compatibility :
tcp_metrics used to export RTT and RTTVAR in msec resolution,
so we added RTT_US and RTTVAR_US. An iproute2 patch is needed
to use the new attributes if provided by the kernel.
In this example ss command displays a srtt of 32 usecs (10Gbit link)
lpk51:~# ./ss -i dst lpk52
Netid State Recv-Q Send-Q Local Address:Port Peer
Address:Port
tcp ESTAB 0 1 10.246.11.51:42959
10.246.11.52:64614
cubic wscale:6,6 rto:201 rtt:0.032/0.001 ato:40 mss:1448
cwnd:10 send
3620.0Mbps pacing_rate 7240.0Mbps unacked:1 rcv_rtt:993 rcv_space:29559
Updated iproute2 ip command displays :
lpk51:~# ./ip tcp_metrics | grep 10.246.11.52
10.246.11.52 age 561.914sec cwnd 10 rtt 274us rttvar 213us source
10.246.11.51
Old binary displays :
lpk51:~# ip tcp_metrics | grep 10.246.11.52
10.246.11.52 age 561.914sec cwnd 10 rtt 250us rttvar 125us source
10.246.11.51
With help from Julian Anastasov, Stephen Hemminger and Yuchung Cheng
Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Cc: Stephen Hemminger <stephen@networkplumber.org>
Cc: Yuchung Cheng <ycheng@google.com>
Cc: Larry Brakmo <brakmo@google.com>
Cc: Julian Anastasov <ja@ssi.bg>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'include/linux/tcp.h')
| -rw-r--r-- | include/linux/tcp.h | 8 |
1 files changed, 4 insertions, 4 deletions
diff --git a/include/linux/tcp.h b/include/linux/tcp.h index 4ad0706d40eb..239946868142 100644 --- a/include/linux/tcp.h +++ b/include/linux/tcp.h @@ -201,10 +201,10 @@ struct tcp_sock { u32 tlp_high_seq; /* snd_nxt at the time of TLP retransmit. */ /* RTT measurement */ - u32 srtt; /* smoothed round trip time << 3 */ - u32 mdev; /* medium deviation */ - u32 mdev_max; /* maximal mdev for the last rtt period */ - u32 rttvar; /* smoothed mdev_max */ + u32 srtt_us; /* smoothed round trip time << 3 in usecs */ + u32 mdev_us; /* medium deviation */ + u32 mdev_max_us; /* maximal mdev for the last rtt period */ + u32 rttvar_us; /* smoothed mdev_max */ u32 rtt_seq; /* sequence number to update rttvar */ u32 packets_out; /* Packets which are "in flight" */ |