Commit Graph

75 Commits

Author SHA1 Message Date
David Vernet 400031e05a bpf: Add __bpf_kfunc tag to all kfuncs
Now that we have the __bpf_kfunc tag, we should use add it to all
existing kfuncs to ensure that they'll never be elided in LTO builds.

Signed-off-by: David Vernet <void@manifault.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Stanislav Fomichev <sdf@google.com>
Link: https://lore.kernel.org/bpf/20230201173016.342758-4-void@manifault.com
2023-02-02 00:25:14 +01:00
Kumar Kartikeya Dwivedi a4703e3184 bpf: Switch to new kfunc flags infrastructure
Instead of populating multiple sets to indicate some attribute and then
researching the same BTF ID in them, prepare a single unified BTF set
which indicates whether a kfunc is allowed to be called, and also its
attributes if any at the same time. Now, only one call is needed to
perform the lookup for both kfunc availability and its attributes.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20220721134245.2450-4-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
2022-07-21 20:59:42 -07:00
Eric Dumazet 9957b38b5e tcp_cubic: make hystart_ack_delay() aware of BIG TCP
hystart_ack_delay() had the assumption that a TSO packet
would not be bigger than GSO_MAX_SIZE.

This will no longer be true.

We should use sk->sk_gso_max_size instead.

This reduces chances of spurious Hystart ACK train detections.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Alexander Duyck <alexanderduyck@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
2022-05-16 10:18:56 +01:00
Eric Dumazet 4057037535 tcp: add accessors to read/set tp->snd_cwnd
We had various bugs over the years with code
breaking the assumption that tp->snd_cwnd is greater
than zero.

Lately, syzbot reported the WARN_ON_ONCE(!tp->prior_cwnd) added
in commit 8b8a321ff7 ("tcp: fix zero cwnd in tcp_cwnd_reduction")
can trigger, and without a repro we would have to spend
considerable time finding the bug.

Instead of complaining too late, we want to catch where
and when tp->snd_cwnd is set to an illegal value.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Suggested-by: Yuchung Cheng <ycheng@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Acked-by: Yuchung Cheng <ycheng@google.com>
Link: https://lore.kernel.org/r/20220405233538.947344-1-eric.dumazet@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
2022-04-06 12:05:41 -07:00
Kumar Kartikeya Dwivedi b202d84422 bpf: Remove check_kfunc_call callback and old kfunc BTF ID API
Completely remove the old code for check_kfunc_call to help it work
with modules, and also the callback itself.

The previous commit adds infrastructure to register all sets and put
them in vmlinux or module BTF, and concatenates all related sets
organized by the hook and the type. Once populated, these sets remain
immutable for the lifetime of the struct btf.

Also, since we don't need the 'owner' module anywhere when doing
check_kfunc_call, drop the 'btf_modp' module parameter from
find_kfunc_desc_btf.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20220114163953.1455836-4-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
2022-01-18 14:26:41 -08:00
Eric Dumazet 4e1fddc98d tcp_cubic: fix spurious Hystart ACK train detections for not-cwnd-limited flows
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: ae27e98a51 ("[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>
2021-11-24 17:26:05 -08:00
Kumar Kartikeya Dwivedi 0e32dfc80b bpf: Enable TCP congestion control kfunc from modules
This commit moves BTF ID lookup into the newly added registration
helper, in a way that the bbr, cubic, and dctcp implementation set up
their sets in the bpf_tcp_ca kfunc_btf_set list, while the ones not
dependent on modules are looked up from the wrapper function.

This lifts the restriction for them to be compiled as built in objects,
and can be loaded as modules if required. Also modify Makefile.modfinal
to call resolve_btfids for each module.

Note that since kernel kfunc_ids never overlap with module kfunc_ids, we
only match the owner for module btf id sets.

See following commits for background on use of:

 CONFIG_X86 ifdef:
 569c484f99 (bpf: Limit static tcp-cc functions in the .BTF_ids list to x86)

 CONFIG_DYNAMIC_FTRACE ifdef:
 7aae231ac9 (bpf: tcp: Limit calling some tcp cc functions to CONFIG_DYNAMIC_FTRACE)

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20211002011757.311265-6-memxor@gmail.com
2021-10-05 17:07:41 -07:00
Martin KaFai Lau d22f6ad187 tcp: Rename bictcp function prefix to cubictcp
The cubic functions in tcp_cubic.c are using the bictcp prefix as
in tcp_bic.c.  This patch gives it the proper name cubictcp
because the later patch will allow the bpf prog to directly
call the cubictcp implementation.  Renaming them will avoid
the name collision when trying to find the intended
one to call during bpf prog load time.

Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210325015155.1545532-1-kafai@fb.com
2021-03-26 20:41:51 -07:00
Yejune Deng f4d133d86a tcp_cubic: use memset and offsetof init
In bictcp_reset(), use memset and offsetof instead of = 0.

Signed-off-by: Yejune Deng <yejune.deng@gmail.com>
Link: https://lore.kernel.org/r/1610597696-128610-1-git-send-email-yejune.deng@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
2021-01-15 20:22:16 -08:00
Neal Cardwell b344579ca8 tcp_cubic: fix spurious HYSTART_DELAY exit upon drop in min RTT
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: ae27e98a51 ("[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>
2020-06-25 16:08:47 -07:00
Eric Dumazet f278b99ca6 tcp_cubic: refactor code to perform a divide only when needed
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: 42f3a8aaae ("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>
2019-12-30 14:44:27 -08:00
Eric Dumazet ede656e846 tcp_cubic: make Hystart aware of pacing
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>
2019-12-27 16:29:14 -08:00
Eric Dumazet 42f3a8aaae tcp_cubic: tweak Hystart detection for short RTT flows
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>
2019-12-27 16:29:14 -08:00
Eric Dumazet cff04e2da3 tcp_cubic: switch bictcp_clock() to usec resolution
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>
2019-12-27 16:29:14 -08:00
Eric Dumazet 35821fc2b4 tcp_cubic: remove one conditional from hystart_update()
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>
2019-12-27 16:29:14 -08:00
Eric Dumazet 473900a504 tcp_cubic: optimize hystart_update()
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>
2019-12-27 16:29:14 -08:00
Thomas Gleixner 09c434b8a0 treewide: Add SPDX license identifier for more missed files
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>
2019-05-21 10:50:45 +02:00
Yuchung Cheng f1722a1be1 tcp: consolidate congestion control undo functions
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>
2017-08-06 21:25:10 -07:00
Eric Dumazet ac35f56220 tcp: bic, cubic: use tcp_jiffies32 instead of tcp_time_stamp
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>
2017-05-17 16:06:01 -04:00
Eric Dumazet d635fbe27e tcp: use tcp_jiffies32 to feed tp->lsndtime
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>
2017-05-17 16:06:01 -04:00
Chema Gonzalez d6ecf32805 tcp_cubic: fix typo in module param description
Signed-off-by: Chema Gonzalez <chemag@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
2017-04-20 16:16:44 -04:00
Lawrence Brakmo 756ee1729b tcp: replace cnt & rtt with struct in pkts_acked()
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>
2016-05-11 14:43:19 -04:00
Eric Dumazet c10d9310ed tcp: do not assume TCP code is non preemptible
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>
2016-05-02 17:02:25 -04:00
Eric Dumazet 02a1d6e7a6 net: rename NET_{ADD|INC}_STATS_BH()
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>
2016-04-27 22:48:24 -04:00
Eric Dumazet c2e7204d18 tcp_cubic: do not set epoch_start in the future
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: 30927520db ("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>
2015-09-17 22:35:07 -07:00
Eric Dumazet 30927520db tcp_cubic: better follow cubic curve after idle period
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>
2015-09-10 10:58:33 -07:00
Yuchung Cheng 071d5080e3 tcp: add tcp_in_slow_start helper
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>
2015-07-09 14:22:52 -07:00
Neal Cardwell d578e18ce9 tcp: restore 1.5x per RTT limit to CUBIC cwnd growth in congestion avoidance
Commit 814d488c61 ("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: 9cd981dcf1 ("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>
2015-03-11 16:51:51 -04:00
Neal Cardwell d6b1a8a92a tcp: fix timing issue in CUBIC slope calculation
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>
2015-01-28 22:18:38 -08:00
Neal Cardwell 9cd981dcf1 tcp: fix stretch ACK bugs in CUBIC
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>
2015-01-28 22:18:38 -08:00
Neal Cardwell e73ebb0881 tcp: stretch ACK fixes prep
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>
2015-01-28 22:18:37 -08:00
Eric Dumazet 42eef7a0bb tcp_cubic: refine Hystart delay threshold
In commit 2b4636a5f8 ("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>
2014-12-09 14:58:23 -05:00
Eric Dumazet 6e3a8a937c tcp_cubic: add SNMP counters to track how effective is Hystart
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>
2014-12-09 14:58:23 -05:00
stephen hemminger 688d1945bc tcp: whitespace fixes
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>
2014-09-01 18:12:45 -07:00
David S. Miller 5f013c9bc7 Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net
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>
2014-05-12 13:19:14 -04:00
Eric Dumazet 249015515f tcp: remove in_flight parameter from cong_avoid() methods
Commit e114a710aa ("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>
2014-05-03 19:23:07 -04:00
Liu Yu 0cda345d1b tcp_cubic: fix the range of delayed_ack
commit b9f47a3aae (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 5b35e1e6e9 (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>
2014-04-30 16:12:22 -04:00
Eric Dumazet 740b0f1841 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>
2014-02-26 17:08:40 -05:00
Yuchung Cheng 9f9843a751 tcp: properly handle stretch acks in slow start
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>
2013-11-04 19:57:59 -05:00
Eric Dumazet cd6b423afd tcp: cubic: fix bug in bictcp_acked()
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>
2013-08-07 10:35:08 -07:00
Eric Dumazet 2ed0edf909 tcp: cubic: fix overflow error in bictcp_update()
commit 17a6e9f1aa ("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>
2013-08-07 10:35:05 -07:00
Neal Cardwell 5a45f0086a tcp: fix undo after RTO for CUBIC
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>
2012-01-20 14:17:26 -05:00
stephen hemminger b9f47a3aae tcp_cubic: limit delayed_ack ratio to prevent divide error
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>
2011-05-08 15:51:57 -07:00
David S. Miller c337ffb68e Merge branch 'master' of master.kernel.org:/pub/scm/linux/kernel/git/davem/net-2.6 2011-03-15 15:15:17 -07:00
Sangtae Ha b5ccd07337 tcp_cubic: fix low utilization of CUBIC with HyStart
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>
2011-03-14 15:54:42 -07:00
Sangtae Ha 2b4636a5f8 tcp_cubic: make the delay threshold of HyStart less sensitive
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>
2011-03-14 15:54:42 -07:00
stephen hemminger 3b585b3449 tcp_cubic: enable high resolution ack time if needed
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>
2011-03-14 15:54:40 -07:00
stephen hemminger 17a6e9f1aa tcp_cubic: fix clock dependency
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>
2011-03-14 15:54:39 -07:00
stephen hemminger aac46324e1 tcp_cubic: make ack train delta value a parameter
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>
2011-03-14 15:54:39 -07:00
stephen hemminger c54b4b7655 tcp_cubic: fix comparison of jiffies
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>
2011-03-14 15:54:38 -07:00