1. 11 Jan, 2016 1 commit
  2. 28 Jan, 2015 1 commit
    • Neal Cardwell's avatar
      tcp: stretch ACK fixes prep · e73ebb08
      Neal Cardwell authored
      
      
      LRO, GRO, delayed ACKs, and middleboxes can cause "stretch ACKs" that
      cover more than the RFC-specified maximum of 2 packets. These stretch
      ACKs can cause serious performance shortfalls in common congestion
      control algorithms that were designed and tuned years ago with
      receiver hosts that were not using LRO or GRO, and were instead
      politely ACKing every other packet.
      
      This patch series fixes Reno and CUBIC to handle stretch ACKs.
      
      This patch prepares for the upcoming stretch ACK bug fix patches. It
      adds an "acked" parameter to tcp_cong_avoid_ai() to allow for future
      fixes to tcp_cong_avoid_ai() to correctly handle stretch ACKs, and
      changes all congestion control algorithms to pass in 1 for the ACKed
      count. It also changes tcp_slow_start() to return the number of packet
      ACK "credits" that were not processed in slow start mode, and can be
      processed by the congestion control module in additive increase mode.
      
      In future patches we will fix tcp_cong_avoid_ai() to handle stretch
      ACKs, and fix Reno and CUBIC handling of stretch ACKs in slow start
      and additive increase mode.
      Reported-by: default avatarEyal Perry <eyalpe@mellanox.com>
      Signed-off-by: default avatarNeal Cardwell <ncardwell@google.com>
      Signed-off-by: default avatarYuchung Cheng <ycheng@google.com>
      Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      e73ebb08
  3. 01 Sep, 2014 1 commit
  4. 03 May, 2014 1 commit
  5. 26 Feb, 2014 1 commit
    • Eric Dumazet's avatar
      tcp: switch rtt estimations to usec resolution · 740b0f18
      Eric Dumazet authored
      
      
      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: default avatarEric Dumazet <edumazet@google.com>
      Acked-by: default avatarNeal 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: default avatarDavid S. Miller <davem@davemloft.net>
      740b0f18
  6. 13 Feb, 2014 1 commit
  7. 26 Dec, 2013 2 commits
  8. 04 Nov, 2013 1 commit
    • Yuchung Cheng's avatar
      tcp: properly handle stretch acks in slow start · 9f9843a7
      Yuchung Cheng authored
      
      
      Slow start now increases cwnd by 1 if an ACK acknowledges some packets,
      regardless the number of packets. Consequently slow start performance
      is highly dependent on the degree of the stretch ACKs caused by
      receiver or network ACK compression mechanisms (e.g., delayed-ACK,
      GRO, etc).  But slow start algorithm is to send twice the amount of
      packets of packets left so it should process a stretch ACK of degree
      N as if N ACKs of degree 1, then exits when cwnd exceeds ssthresh. A
      follow up patch will use the remainder of the N (if greater than 1)
      to adjust cwnd in the congestion avoidance phase.
      
      In addition this patch retires the experimental limited slow start
      (LSS) feature. LSS has multiple drawbacks but questionable benefit. The
      fractional cwnd increase in LSS requires a loop in slow start even
      though it's rarely used. Configuring such an increase step via a global
      sysctl on different BDPS seems hard. Finally and most importantly the
      slow start overshoot concern is now better covered by the Hybrid slow
      start (hystart) enabled by default.
      Signed-off-by: default avatarYuchung Cheng <ycheng@google.com>
      Signed-off-by: default avatarNeal Cardwell <ncardwell@google.com>
      Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      9f9843a7
  9. 31 Mar, 2011 1 commit
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  17. 25 Apr, 2007 5 commits