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2021-12-01tcp_cubic: fix spurious Hystart ACK train detections for not-cwnd-limited flowsEric Dumazet1-2/+3
[ Upstream commit 4e1fddc98d2585ddd4792b5e44433dcee7ece001 ] While testing BIG TCP patch series, I was expecting that TCP_RR workloads with 80KB requests/answers would send one 80KB TSO packet, then being received as a single GRO packet. It turns out this was not happening, and the root cause was that cubic Hystart ACK train was triggering after a few (2 or 3) rounds of RPC. Hystart was wrongly setting CWND/SSTHRESH to 30, while my RPC needed a budget of ~20 segments. Ideally these TCP_RR flows should not exit slow start. Cubic Hystart should reset itself at each round, instead of assuming every TCP flow is a bulk one. Note that even after this patch, Hystart can still trigger, depending on scheduling artifacts, but at a higher CWND/SSTHRESH threshold, keeping optimal TSO packet sizes. Tested: ip link set dev eth0 gro_ipv6_max_size 131072 gso_ipv6_max_size 131072 nstat -n; netperf -H ... -t TCP_RR -l 5 -- -r 80000,80000 -K cubic; nstat|egrep "Ip6InReceives|Hystart|Ip6OutRequests" Before: 8605 Ip6InReceives 87541 0.0 Ip6OutRequests 129496 0.0 TcpExtTCPHystartTrainDetect 1 0.0 TcpExtTCPHystartTrainCwnd 30 0.0 After: 8760 Ip6InReceives 88514 0.0 Ip6OutRequests 87975 0.0 Fixes: ae27e98a5152 ("[TCP] CUBIC v2.3") Co-developed-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Cc: Stephen Hemminger <stephen@networkplumber.org> Cc: Yuchung Cheng <ycheng@google.com> Cc: Soheil Hassas Yeganeh <soheil@google.com> Link: https://lore.kernel.org/r/20211123202535.1843771-1-eric.dumazet@gmail.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> Signed-off-by: Sasha Levin <sashal@kernel.org>
2020-06-26tcp_cubic: fix spurious HYSTART_DELAY exit upon drop in min RTTNeal Cardwell1-3/+2
Mirja Kuehlewind reported a bug in Linux TCP CUBIC Hystart, where Hystart HYSTART_DELAY mechanism can exit Slow Start spuriously on an ACK when the minimum rtt of a connection goes down. From inspection it is clear from the existing code that this could happen in an example like the following: o The first 8 RTT samples in a round trip are 150ms, resulting in a curr_rtt of 150ms and a delay_min of 150ms. o The 9th RTT sample is 100ms. The curr_rtt does not change after the first 8 samples, so curr_rtt remains 150ms. But delay_min can be lowered at any time, so delay_min falls to 100ms. The code executes the HYSTART_DELAY comparison between curr_rtt of 150ms and delay_min of 100ms, and the curr_rtt is declared far enough above delay_min to force a (spurious) exit of Slow start. The fix here is simple: allow every RTT sample in a round trip to lower the curr_rtt. Fixes: ae27e98a5152 ("[TCP] CUBIC v2.3") Reported-by: Mirja Kuehlewind <mirja.kuehlewind@ericsson.com> Signed-off-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Acked-by: Soheil Hassas Yeganeh <soheil@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2019-12-31tcp_cubic: refactor code to perform a divide only when neededEric Dumazet1-23/+28
Neal Cardwell suggested to not change ca->delay_min and apply the ack delay cushion only when Hystart ACK train is still under consideration. This should avoid a 64bit divide unless needed. Tested: 40Gbit(mlx4) testbed (with sch_fq as packet scheduler) $ echo -n 'file tcp_cubic.c +p' >/sys/kernel/debug/dynamic_debug/control $ nstat -n;for f in {1..10}; do ./super_netperf 1 -H lpaa24 -l -4000000; done;nstat|egrep "Hystart" 14815 16280 15293 15563 11574 15145 14789 18548 16972 12520 TcpExtTCPHystartTrainDetect 10 0.0 TcpExtTCPHystartTrainCwnd 1396 0.0 $ dmesg | tail -10 [ 4873.951350] hystart_ack_train (116 > 93) delay_min 24 (+ ack_delay 69) cwnd 80 [ 4875.155379] hystart_ack_train (55 > 50) delay_min 21 (+ ack_delay 29) cwnd 160 [ 4876.333921] hystart_ack_train (69 > 62) delay_min 23 (+ ack_delay 39) cwnd 130 [ 4877.519037] hystart_ack_train (69 > 60) delay_min 22 (+ ack_delay 38) cwnd 130 [ 4878.701559] hystart_ack_train (87 > 63) delay_min 24 (+ ack_delay 39) cwnd 160 [ 4879.844597] hystart_ack_train (93 > 50) delay_min 21 (+ ack_delay 29) cwnd 216 [ 4880.956650] hystart_ack_train (74 > 67) delay_min 20 (+ ack_delay 47) cwnd 108 [ 4882.098500] hystart_ack_train (61 > 57) delay_min 23 (+ ack_delay 34) cwnd 130 [ 4883.262056] hystart_ack_train (72 > 67) delay_min 21 (+ ack_delay 46) cwnd 130 [ 4884.418760] hystart_ack_train (74 > 67) delay_min 29 (+ ack_delay 38) cwnd 152 10Gbit(bnx2x) testbed (with sch_fq as packet scheduler) $ echo -n 'file tcp_cubic.c +p' >/sys/kernel/debug/dynamic_debug/control $ nstat -n;for f in {1..10}; do ./super_netperf 1 -H lpk52 -l -4000000; done;nstat|egrep "Hystart" 7050 7065 7100 6900 7202 7263 7189 6869 7463 7034 TcpExtTCPHystartTrainDetect 10 0.0 TcpExtTCPHystartTrainCwnd 3199 0.0 $ dmesg | tail -10 [ 176.920012] hystart_ack_train (161 > 141) delay_min 83 (+ ack_delay 58) cwnd 264 [ 179.144645] hystart_ack_train (164 > 159) delay_min 120 (+ ack_delay 39) cwnd 444 [ 181.354527] hystart_ack_train (214 > 168) delay_min 125 (+ ack_delay 43) cwnd 436 [ 183.539565] hystart_ack_train (170 > 147) delay_min 96 (+ ack_delay 51) cwnd 326 [ 185.727309] hystart_ack_train (177 > 160) delay_min 61 (+ ack_delay 99) cwnd 128 [ 187.947142] hystart_ack_train (184 > 167) delay_min 123 (+ ack_delay 44) cwnd 367 [ 190.166680] hystart_ack_train (230 > 153) delay_min 116 (+ ack_delay 37) cwnd 444 [ 192.327285] hystart_ack_train (210 > 206) delay_min 86 (+ ack_delay 120) cwnd 152 [ 194.511392] hystart_ack_train (173 > 151) delay_min 94 (+ ack_delay 57) cwnd 239 [ 196.736023] hystart_ack_train (149 > 146) delay_min 105 (+ ack_delay 41) cwnd 399 Fixes: 42f3a8aaae66 ("tcp_cubic: tweak Hystart detection for short RTT flows") Signed-off-by: Eric Dumazet <edumazet@google.com> Reported-by: Neal Cardwell <ncardwell@google.com> Link: https://www.spinics.net/lists/netdev/msg621886.html Link: https://www.spinics.net/lists/netdev/msg621797.html Acked-by: Neal Cardwell <ncardwell@google.com> Acked-by: Soheil Hassas Yeganeh <soheil@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2019-12-28tcp_cubic: make Hystart aware of pacingEric Dumazet1-1/+12
For years we disabled Hystart ACK train detection at Google because it was fooled by TCP pacing. ACK train detection uses a simple heuristic, detecting if we receive ACK past half the RTT, to exit slow start before hitting the bottleneck and experience massive drops. But pacing by design might delay packets up to RTT/2, so we need to tweak the Hystart logic to be aware of this extra delay. Tested: Added a 100 usec delay at receiver. Before: nstat -n;for f in {1..10}; do ./super_netperf 1 -H lpaa24 -l -4000000; done;nstat|egrep "Hystart" 9117 7057 9553 8300 7030 6849 9533 10126 6876 8473 TcpExtTCPHystartTrainDetect 10 0.0 TcpExtTCPHystartTrainCwnd 1230 0.0 After : nstat -n;for f in {1..10}; do ./super_netperf 1 -H lpaa24 -l -4000000; done;nstat|egrep "Hystart" 9845 10103 10866 11096 11936 11487 11773 12188 11066 11894 TcpExtTCPHystartTrainDetect 10 0.0 TcpExtTCPHystartTrainCwnd 6462 0.0 Disabling Hystart ACK Train detection gives similar numbers echo 2 >/sys/module/tcp_cubic/parameters/hystart_detect nstat -n;for f in {1..10}; do ./super_netperf 1 -H lpaa24 -l -4000000; done;nstat|egrep "Hystart" 11173 10954 12455 10627 11578 11583 11222 10880 10665 11366 Signed-off-by: Eric Dumazet <edumazet@google.com> Acked-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2019-12-28tcp_cubic: tweak Hystart detection for short RTT flowsEric Dumazet1-2/+21
After switching ca->delay_min to usec resolution, we exit slow start prematurely for very low RTT flows, setting snd_ssthresh to 20. The reason is that delay_min is fed with RTT of small packet trains. Then as cwnd is increased, TCP sends bigger TSO packets. LRO/GRO aggregation and/or interrupt mitigation strategies on receiver tend to inflate RTT samples. Fix this by adding to delay_min the expected delay of two TSO packets, given current pacing rate. Tested: Sender uses pfifo_fast qdisc Before : $ nstat -n;for f in {1..10}; do ./super_netperf 1 -H lpaa24 -l -4000000; done;nstat|egrep "Hystart" 11348 11707 11562 11428 11773 11534 9878 11693 10597 10968 TcpExtTCPHystartTrainDetect 10 0.0 TcpExtTCPHystartTrainCwnd 200 0.0 After : $ nstat -n;for f in {1..10}; do ./super_netperf 1 -H lpaa24 -l -4000000; done;nstat|egrep "Hystart" 14877 14517 15797 18466 17376 14833 17558 17933 16039 18059 TcpExtTCPHystartTrainDetect 10 0.0 TcpExtTCPHystartTrainCwnd 1670 0.0 Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2019-12-28tcp_cubic: switch bictcp_clock() to usec resolutionEric Dumazet1-21/+14
Current 1ms clock feeds ca->round_start, ca->delay_min, ca->last_ack. This is quite problematic for data-center flows, where delay_min is way below 1 ms. This means Hystart Train detection triggers every time jiffies value is updated, since "((s32)(now - ca->round_start) > ca->delay_min >> 4)" expression becomes true. This kind of random behavior can be solved by reusing the existing usec timestamp that TCP keeps in tp->tcp_mstamp Note that a followup patch will tweak things a bit, because during slow start, GRO aggregation on receivers naturally increases the RTT as TSO packets gradually come to ~64KB size. To recap, right after this patch CUBIC Hystart train detection is more aggressive, since short RTT flows might exit slow start at cwnd = 20, instead of being possibly unbounded. Following patch will address this problem. Signed-off-by: Eric Dumazet <edumazet@google.com> Acked-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2019-12-28tcp_cubic: remove one conditional from hystart_update()Eric Dumazet1-2/+2
If we initialize ca->curr_rtt to ~0U, we do not need to test for zero value in hystart_update() We only read ca->curr_rtt if at least HYSTART_MIN_SAMPLES have been processed, and thus ca->curr_rtt will have a sane value. Signed-off-by: Eric Dumazet <edumazet@google.com> Acked-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2019-12-28tcp_cubic: optimize hystart_update()Eric Dumazet1-6/+3
We do not care which bit in ca->found is set. We avoid accessing hystart and hystart_detect unless really needed, possibly avoiding one cache line miss. Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2019-05-21treewide: Add SPDX license identifier for more missed filesThomas Gleixner1-0/+1
Add SPDX license identifiers to all files which: - Have no license information of any form - Have MODULE_LICENCE("GPL*") inside which was used in the initial scan/conversion to ignore the file These files fall under the project license, GPL v2 only. The resulting SPDX license identifier is: GPL-2.0-only Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2017-08-07tcp: consolidate congestion control undo functionsYuchung Cheng1-12/+1
Most TCP congestion controls are using identical logic to undo cwnd except BBR. This patch consolidates these similar functions to the one used currently by Reno and others. Suggested-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: Yuchung Cheng <ycheng@google.com> Signed-off-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2017-05-17tcp: bic, cubic: use tcp_jiffies32 instead of tcp_time_stampEric Dumazet1-6/+6
Use tcp_jiffies32 instead of tcp_time_stamp, since tcp_time_stamp will soon be only used for TCP TS option. Signed-off-by: Eric Dumazet <edumazet@google.com> Acked-by: Soheil Hassas Yeganeh <soheil@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2017-05-17tcp: use tcp_jiffies32 to feed tp->lsndtimeEric Dumazet1-1/+1
Use tcp_jiffies32 instead of tcp_time_stamp to feed tp->lsndtime. tcp_time_stamp will soon be a litle bit more expensive than simply reading 'jiffies'. Signed-off-by: Eric Dumazet <edumazet@google.com> Acked-by: Soheil Hassas Yeganeh <soheil@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2017-04-20tcp_cubic: fix typo in module param descriptionChema Gonzalez1-1/+1
Signed-off-by: Chema Gonzalez <chemag@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-11tcp: replace cnt & rtt with struct in pkts_acked()Lawrence Brakmo1-3/+3
Replace 2 arguments (cnt and rtt) in the congestion control modules' pkts_acked() function with a struct. This will allow adding more information without having to modify existing congestion control modules (tcp_nv in particular needs bytes in flight when packet was sent). As proposed by Neal Cardwell in his comments to the tcp_nv patch. Signed-off-by: Lawrence Brakmo <brakmo@fb.com> Acked-by: Yuchung Cheng <ycheng@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-05-03tcp: do not assume TCP code is non preemptibleEric Dumazet1-10/+10
We want to to make TCP stack preemptible, as draining prequeue and backlog queues can take lot of time. Many SNMP updates were assuming that BH (and preemption) was disabled. Need to convert some __NET_INC_STATS() calls to NET_INC_STATS() and some __TCP_INC_STATS() to TCP_INC_STATS() Before using this_cpu_ptr(net->ipv4.tcp_sk) in tcp_v4_send_reset() and tcp_v4_send_ack(), we add an explicit preempt disabled section. Signed-off-by: Eric Dumazet <edumazet@google.com> Acked-by: Soheil Hassas Yeganeh <soheil@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2016-04-28net: rename NET_{ADD|INC}_STATS_BH()Eric Dumazet1-10/+10
Rename NET_INC_STATS_BH() to __NET_INC_STATS() and NET_ADD_STATS_BH() to __NET_ADD_STATS() Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-09-18tcp_cubic: do not set epoch_start in the futureEric Dumazet1-2/+8
Tracking idle time in bictcp_cwnd_event() is imprecise, as epoch_start is normally set at ACK processing time, not at send time. Doing a proper fix would need to add an additional state variable, and does not seem worth the trouble, given CUBIC bug has been there forever before Jana noticed it. Let's simply not set epoch_start in the future, otherwise bictcp_update() could overflow and CUBIC would again grow cwnd too fast. This was detected thanks to a packetdrill test Neal wrote that was flaky before applying this fix. Fixes: 30927520dbae ("tcp_cubic: better follow cubic curve after idle period") Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: Yuchung Cheng <ycheng@google.com> Cc: Jana Iyengar <jri@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-09-10tcp_cubic: better follow cubic curve after idle periodEric Dumazet1-0/+16
Jana Iyengar found an interesting issue on CUBIC : The epoch is only updated/reset initially and when experiencing losses. The delta "t" of now - epoch_start can be arbitrary large after app idle as well as the bic_target. Consequentially the slope (inverse of ca->cnt) would be really large, and eventually ca->cnt would be lower-bounded in the end to 2 to have delayed-ACK slow-start behavior. This particularly shows up when slow_start_after_idle is disabled as a dangerous cwnd inflation (1.5 x RTT) after few seconds of idle time. Jana initial fix was to reset epoch_start if app limited, but Neal pointed out it would ask the CUBIC algorithm to recalculate the curve so that we again start growing steeply upward from where cwnd is now (as CUBIC does just after a loss). Ideally we'd want the cwnd growth curve to be the same shape, just shifted later in time by the amount of the idle period. Reported-by: Jana Iyengar <jri@google.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: Yuchung Cheng <ycheng@google.com> Signed-off-by: Neal Cardwell <ncardwell@google.com> Cc: Stephen Hemminger <stephen@networkplumber.org> Cc: Sangtae Ha <sangtae.ha@gmail.com> Cc: Lawrence Brakmo <lawrence@brakmo.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-07-10tcp: add tcp_in_slow_start helperYuchung Cheng1-2/+2
Add a helper to test the slow start condition in various congestion control modules and other places. This is to prepare a slight improvement in policy as to exactly when to slow start. Signed-off-by: Yuchung Cheng <ycheng@google.com> Signed-off-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: Nandita Dukkipati <nanditad@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-03-11tcp: restore 1.5x per RTT limit to CUBIC cwnd growth in congestion avoidanceNeal Cardwell1-2/+4
Commit 814d488c6126 ("tcp: fix the timid additive increase on stretch ACKs") fixed a bug where tcp_cong_avoid_ai() would either credit a connection with an increase of snd_cwnd_cnt, or increase snd_cwnd, but not both, resulting in cwnd increasing by 1 packet on at most every alternate invocation of tcp_cong_avoid_ai(). Although the commit correctly implemented the CUBIC algorithm, which can increase cwnd by as much as 1 packet per 1 packet ACKed (2x per RTT), in practice that could be too aggressive: in tests on network paths with small buffers, YouTube server retransmission rates nearly doubled. This commit restores CUBIC to a maximum cwnd growth rate of 1 packet per 2 packets ACKed (1.5x per RTT). In YouTube tests this restored retransmit rates to low levels. Testing: This patch has been tested in datacenter netperf transfers and live youtube.com and google.com servers. Fixes: 9cd981dcf174 ("tcp: fix stretch ACK bugs in CUBIC") Signed-off-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: Yuchung Cheng <ycheng@google.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-01-29tcp: fix timing issue in CUBIC slope calculationNeal Cardwell1-0/+8
This patch fixes a bug in CUBIC that causes cwnd to increase slightly too slowly when multiple ACKs arrive in the same jiffy. If cwnd is supposed to increase at a rate of more than once per jiffy, then CUBIC was sometimes too slow. Because the bic_target is calculated for a future point in time, calculated with time in jiffies, the cwnd can increase over the course of the jiffy while the bic_target calculated as the proper CUBIC cwnd at time t=tcp_time_stamp+rtt does not increase, because tcp_time_stamp only increases on jiffy tick boundaries. So since the cnt is set to: ca->cnt = cwnd / (bic_target - cwnd); as cwnd increases but bic_target does not increase due to jiffy granularity, the cnt becomes too large, causing cwnd to increase too slowly. For example: - suppose at the beginning of a jiffy, cwnd=40, bic_target=44 - so CUBIC sets: ca->cnt = cwnd / (bic_target - cwnd) = 40 / (44 - 40) = 40/4 = 10 - suppose we get 10 acks, each for 1 segment, so tcp_cong_avoid_ai() increases cwnd to 41 - so CUBIC sets: ca->cnt = cwnd / (bic_target - cwnd) = 41 / (44 - 41) = 41 / 3 = 13 So now CUBIC will wait for 13 packets to be ACKed before increasing cwnd to 42, insted of 10 as it should. The fix is to avoid adjusting the slope (determined by ca->cnt) multiple times within a jiffy, and instead skip to compute the Reno cwnd, the "TCP friendliness" code path. Reported-by: Eyal Perry <eyalpe@mellanox.com> Signed-off-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: Yuchung Cheng <ycheng@google.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-01-29tcp: fix stretch ACK bugs in CUBICNeal Cardwell1-22/+9
Change CUBIC to properly handle stretch ACKs in additive increase mode by passing in the count of ACKed packets to tcp_cong_avoid_ai(). In addition, because we are now precisely accounting for stretch ACKs, including delayed ACKs, we can now remove the delayed ACK tracking and estimation code that tracked recent delayed ACK behavior in ca->delayed_ack. Reported-by: Eyal Perry <eyalpe@mellanox.com> Signed-off-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: Yuchung Cheng <ycheng@google.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2015-01-29tcp: stretch ACK fixes prepNeal Cardwell1-1/+1
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: Eyal Perry <eyalpe@mellanox.com> Signed-off-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: Yuchung Cheng <ycheng@google.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-12-09tcp_cubic: refine Hystart delay thresholdEric Dumazet1-1/+1
In commit 2b4636a5f8ca ("tcp_cubic: make the delay threshold of HyStart less sensitive"), HYSTART_DELAY_MIN was changed to 4 ms. The remaining problem is that using delay_min + (delay_min/16) as the threshold is too sensitive. 6.25 % of variation is too small for rtt above 60 ms, which are not uncommon. Lets use 12.5 % instead (delay_min + (delay_min/8)) Tested: 80 ms RTT between peers, FQ/pacing packet scheduler on sender. 10 bulk transfers of 10 seconds : nstat >/dev/null for i in `seq 1 10` do netperf -H remote -- -k THROUGHPUT | grep THROUGHPUT done nstat | grep Hystart With the 6.25 % threshold : THROUGHPUT=20.66 THROUGHPUT=249.38 THROUGHPUT=254.10 THROUGHPUT=14.94 THROUGHPUT=251.92 THROUGHPUT=237.73 THROUGHPUT=19.18 THROUGHPUT=252.89 THROUGHPUT=21.32 THROUGHPUT=15.58 TcpExtTCPHystartTrainDetect 2 0.0 TcpExtTCPHystartTrainCwnd 4756 0.0 TcpExtTCPHystartDelayDetect 5 0.0 TcpExtTCPHystartDelayCwnd 180 0.0 With the 12.5 % threshold THROUGHPUT=251.09 THROUGHPUT=247.46 THROUGHPUT=250.92 THROUGHPUT=248.91 THROUGHPUT=250.88 THROUGHPUT=249.84 THROUGHPUT=250.51 THROUGHPUT=254.15 THROUGHPUT=250.62 THROUGHPUT=250.89 TcpExtTCPHystartTrainDetect 1 0.0 TcpExtTCPHystartTrainCwnd 3175 0.0 Signed-off-by: Eric Dumazet <edumazet@google.com> Acked-by: Neal Cardwell <ncardwell@google.com> Tested-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-12-09tcp_cubic: add SNMP counters to track how effective is HystartEric Dumazet1-9/+22
When deploying FQ pacing, one thing we noticed is that CUBIC Hystart triggers too soon. Having SNMP counters to have an idea of how often the various Hystart methods trigger is useful prior to any modifications. This patch adds SNMP counters tracking, how many time "ack train" or "Delay" based Hystart triggers, and cumulative sum of cwnd at the time Hystart decided to end SS (Slow Start) myhost:~# nstat -a | grep Hystart TcpExtTCPHystartTrainDetect 9 0.0 TcpExtTCPHystartTrainCwnd 20650 0.0 TcpExtTCPHystartDelayDetect 10 0.0 TcpExtTCPHystartDelayCwnd 360 0.0 -> Train detection was triggered 9 times, and average cwnd was 20650/9=2294, Delay detection was triggered 10 times and average cwnd was 36 Signed-off-by: Eric Dumazet <edumazet@google.com> Acked-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-09-02tcp: whitespace fixesstephen hemminger1-8/+10
Fix places where there is space before tab, long lines, and awkward if(){, double spacing etc. Add blank line after declaration/initialization. Signed-off-by: Stephen Hemminger <stephen@networkplumber.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-05-12Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/netDavid S. Miller1-1/+1
Conflicts: drivers/net/ethernet/altera/altera_sgdma.c net/netlink/af_netlink.c net/sched/cls_api.c net/sched/sch_api.c The netlink conflict dealt with moving to netlink_capable() and netlink_ns_capable() in the 'net' tree vs. supporting 'tc' operations in non-init namespaces. These were simple transformations from netlink_capable to netlink_ns_capable. The Altera driver conflict was simply code removal overlapping some void pointer cast cleanups in net-next. Signed-off-by: David S. Miller <davem@davemloft.net>
2014-05-04tcp: remove in_flight parameter from cong_avoid() methodsEric Dumazet1-3/+2
Commit e114a710aa505 ("tcp: fix cwnd limited checking to improve congestion control") obsoleted in_flight parameter from tcp_is_cwnd_limited() and its callers. This patch does the removal as promised. Signed-off-by: Eric Dumazet <edumazet@google.com> Acked-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-05-01tcp_cubic: fix the range of delayed_ackLiu Yu1-1/+1
commit b9f47a3aaeab (tcp_cubic: limit delayed_ack ratio to prevent divide error) try to prevent divide error, but there is still a little chance that delayed_ack can reach zero. In case the param cnt get negative value, then ratio+cnt would overflow and may happen to be zero. As a result, min(ratio, ACK_RATIO_LIMIT) will calculate to be zero. In some old kernels, such as 2.6.32, there is a bug that would pass negative param, which then ultimately leads to this divide error. commit 5b35e1e6e9c (tcp: fix tcp_trim_head() to adjust segment count with skb MSS) fixed the negative param issue. However, it's safe that we fix the range of delayed_ack as well, to make sure we do not hit a divide by zero. CC: Stephen Hemminger <shemminger@vyatta.com> Signed-off-by: Liu Yu <allanyuliu@tencent.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Acked-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2014-02-27tcp: switch rtt estimations to usec resolutionEric Dumazet1-4/+0
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>
2013-11-05tcp: properly handle stretch acks in slow startYuchung Cheng1-2/+3
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: Yuchung Cheng <ycheng@google.com> Signed-off-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2013-08-07tcp: cubic: fix bug in bictcp_acked()Eric Dumazet1-1/+1
While investigating about strange increase of retransmit rates on hosts ~24 days after boot, Van found hystart was disabled if ca->epoch_start was 0, as following condition is true when tcp_time_stamp high order bit is set. (s32)(tcp_time_stamp - ca->epoch_start) < HZ Quoting Van : At initialization & after every loss ca->epoch_start is set to zero so I believe that the above line will turn off hystart as soon as the 2^31 bit is set in tcp_time_stamp & hystart will stay off for 24 days. I think we've observed that cubic's restart is too aggressive without hystart so this might account for the higher drop rate we observe. Diagnosed-by: Van Jacobson <vanj@google.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Cc: Neal Cardwell <ncardwell@google.com> Cc: Yuchung Cheng <ycheng@google.com> Acked-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2013-08-07tcp: cubic: fix overflow error in bictcp_update()Eric Dumazet1-4/+6
commit 17a6e9f1aa9 ("tcp_cubic: fix clock dependency") added an overflow error in bictcp_update() in following code : /* change the unit from HZ to bictcp_HZ */ t = ((tcp_time_stamp + msecs_to_jiffies(ca->delay_min>>3) - ca->epoch_start) << BICTCP_HZ) / HZ; Because msecs_to_jiffies() being unsigned long, compiler does implicit type promotion. We really want to constrain (tcp_time_stamp - ca->epoch_start) to a signed 32bit value, or else 't' has unexpected high values. This bugs triggers an increase of retransmit rates ~24 days after boot [1], as the high order bit of tcp_time_stamp flips. [1] for hosts with HZ=1000 Big thanks to Van Jacobson for spotting this problem. Diagnosed-by: Van Jacobson <vanj@google.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Cc: Neal Cardwell <ncardwell@google.com> Cc: Yuchung Cheng <ycheng@google.com> Cc: Stephen Hemminger <stephen@networkplumber.org> Acked-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2012-01-20tcp: fix undo after RTO for CUBICNeal Cardwell1-4/+6
This patch fixes CUBIC so that cwnd reductions made during RTOs can be undone (just as they already can be undone when using the default/Reno behavior). When undoing cwnd reductions, BIC-derived congestion control modules were restoring the cwnd from last_max_cwnd. There were two problems with using last_max_cwnd to restore a cwnd during undo: (a) last_max_cwnd was set to 0 on state transitions into TCP_CA_Loss (by calling the module's reset() functions), so cwnd reductions from RTOs could not be undone. (b) when fast_covergence is enabled (which it is by default) last_max_cwnd does not actually hold the value of snd_cwnd before the loss; instead, it holds a scaled-down version of snd_cwnd. This patch makes the following changes: (1) upon undo, revert snd_cwnd to ca->loss_cwnd, which is already, as the existing comment notes, the "congestion window at last loss" (2) stop forgetting ca->loss_cwnd on TCP_CA_Loss events (3) use ca->last_max_cwnd to check if we're in slow start Signed-off-by: Neal Cardwell <ncardwell@google.com> Acked-by: Stephen Hemminger <shemminger@vyatta.com> Acked-by: Sangtae Ha <sangtae.ha@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2011-05-09tcp_cubic: limit delayed_ack ratio to prevent divide errorstephen hemminger1-2/+7
TCP Cubic keeps a metric that estimates the amount of delayed acknowledgements to use in adjusting the window. If an abnormally large number of packets are acknowledged at once, then the update could wrap and reach zero. This kind of ACK could only happen when there was a large window and huge number of ACK's were lost. This patch limits the value of delayed ack ratio. The choice of 32 is just a conservative value since normally it should be range of 1 to 4 packets. Signed-off-by: Stephen Hemminger <shemminger@vyatta.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2011-03-16Merge branch 'master' of ↵David S. Miller1-11/+34
master.kernel.org:/pub/scm/linux/kernel/git/davem/net-2.6
2011-03-15tcp_cubic: fix low utilization of CUBIC with HyStartSangtae Ha1-0/+7
HyStart sets the initial exit point of slow start. Suppose that HyStart exits at 0.5BDP in a BDP network and no history exists. If the BDP of a network is large, CUBIC's initial cwnd growth may be too conservative to utilize the link. CUBIC increases the cwnd 20% per RTT in this case. Signed-off-by: Sangtae Ha <sangtae.ha@gmail.com> Acked-by: Stephen Hemminger <shemminger@vyatta.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2011-03-15tcp_cubic: make the delay threshold of HyStart less sensitiveSangtae Ha1-1/+1
Make HyStart less sensitive to abrupt delay variations due to buffer bloat. Signed-off-by: Sangtae Ha <sangtae.ha@gmail.com> Acked-by: Stephen Hemminger <shemminger@vyatta.com> Reported-by: Lucas Nussbaum <lucas.nussbaum@loria.fr> Signed-off-by: David S. Miller <davem@davemloft.net>
2011-03-15tcp_cubic: enable high resolution ack time if neededstephen hemminger1-0/+4
This is a refined version of an earlier patch by Lucas Nussbaum. Cubic needs RTT values in milliseconds. If HZ < 1000 then the values will be too coarse. Signed-off-by: Stephen Hemminger <shemminger@vyatta.com> Reported-by: Lucas Nussbaum <lucas.nussbaum@loria.fr> Signed-off-by: David S. Miller <davem@davemloft.net>
2011-03-15tcp_cubic: fix clock dependencystephen hemminger1-12/+19
The hystart code was written with assumption that HZ=1000. Replace the use of jiffies with bictcp_clock as a millisecond real time clock. Signed-off-by: Stephen Hemminger <shemminger@vyatta.com> Reported-by: Lucas Nussbaum <lucas.nussbaum@loria.fr> Signed-off-by: David S. Miller <davem@davemloft.net>
2011-03-15tcp_cubic: make ack train delta value a parameterstephen hemminger1-1/+4
Make the spacing between ACK's that indicates a train a tuneable value like other hystart values. Signed-off-by: Stephen Hemminger <shemminger@vyatta.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2011-03-15tcp_cubic: fix comparison of jiffiesstephen hemminger1-2/+4
Jiffies wraps around therefore the correct way to compare is to use cast to signed value. Note: cubic is not using full jiffies value on 64 bit arch because using full unsigned long makes struct bictcp grow too large for the available ca_priv area. Includes correction from Sangtae Ha to improve ack train detection. Signed-off-by: Stephen Hemminger <shemminger@vyatta.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2011-03-10tcp: mark tcp_congestion_ops read_mostlyStephen Hemminger1-1/+1
Signed-off-by: Stephen Hemminger <shemminger@vyatta.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2009-03-02tcp: add helper for AI algorithmIlpo Järvinen1-10/+1
It seems that implementation in yeah was inconsistent to what other did as it would increase cwnd one ack earlier than the others do. Size benefits: bictcp_cong_avoid | -36 tcp_cong_avoid_ai | +52 bictcp_cong_avoid | -34 tcp_scalable_cong_avoid | -36 tcp_veno_cong_avoid | -12 tcp_yeah_cong_avoid | -38 = -104 bytes total Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by: David S. Miller <davem@davemloft.net>
2008-11-02[TCP] CUBIC v2.3Sangtae Ha1-11/+109
Signed-off-by: Sangtae Ha <sha2@ncsu.edu> Signed-off-by: David S. Miller <davem@davemloft.net>
2008-05-01rename div64_64 to div64_u64Roman Zippel1-2/+2
Rename div64_64 to div64_u64 to make it consistent with the other divide functions, so it clearly includes the type of the divide. Move its definition to math64.h as currently no architecture overrides the generic implementation. They can still override it of course, but the duplicated declarations are avoided. Signed-off-by: Roman Zippel <zippel@linux-m68k.org> Cc: Avi Kivity <avi@qumranet.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: Geert Uytterhoeven <geert@linux-m68k.org> Cc: Ralf Baechle <ralf@linux-mips.org> Cc: David Howells <dhowells@redhat.com> Cc: Jeff Dike <jdike@addtoit.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: "David S. Miller" <davem@davemloft.net> Cc: Patrick McHardy <kaber@trash.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-03-05[TCP]: TCP cubic v2.2Sangtae Ha1-27/+8
We have updated CUBIC to fix some issues with slow increase in large BDP networks. We also improved its convergence speed. The fix is in fact very simple -- the window increase limit of smax during the window probing phase (i.e., convex growth phase) is removed. We found that this does not affect TCP friendliness, but only improves its scalability. We have run some tests in our lab and also over the Internet path from NCSU to Japan. These results can be seen from the following page: http://netsrv.csc.ncsu.edu/wiki/index.php/Intra_protocol_fairness_testing_with_linux-2.6.23.9 http://netsrv.csc.ncsu.edu/wiki/index.php/RTT_fairness_testing_with_linux-2.6.23.9 http://netsrv.csc.ncsu.edu/wiki/index.php/TCP_friendliness_testing_with_linux-2.6.23.9 Signed-off-by: Sangtae Ha <sha2@ncsu.edu> Signed-off-by: Stephen Hemminger <shemminger@vyatta.com> Signed-off-by: David S. Miller <davem@davemloft.net>
2008-01-29[TCP]: Cong.ctrl modules: remove unused good_ack from cong_avoidIlpo Järvinen1-2/+1
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au> Signed-off-by: David S. Miller <davem@davemloft.net>
2007-10-11[TCP]: Remove num_acked>0 checks from cong.ctrl mods pkts_ackedIlpo Järvinen1-1/+1
There is no need for such check in pkts_acked because the callback is not invoked unless at least one segment got fully ACKed (i.e., the snd_una moved past skb's end_seq) by the cumulative ACK's snd_una advancement. Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by: David S. Miller <davem@davemloft.net>
2007-07-31[TCP]: cubic - eliminate use of receive time stampStephen Hemminger1-28/+18
Remove use of received timestamp option value from RTT calculation in Cubic. A hostile receiver may be returning a larger timestamp option than the original value. This would cause the sender to believe the malevolent receiver had a larger RTT and because Cubic tries to provide some RTT friendliness, the sender would then favor the liar. Instead, use the jiffie resolutionRTT value already computed and passed back after ack. Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org> Signed-off-by: David S. Miller <davem@davemloft.net>
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