kernel/linux.git/net/ipv4/tcp_yeah.c, branch v6.12.80

tcp: add accessors to read/set tp->snd_cwnd

2022-04-06T19:05:41+00:00

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 8b8a321ff72c ("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 Suggested-by: Yuchung Cheng Cc: Neal Cardwell Acked-by: Yuchung Cheng Link: https://lore.kernel.org/r/20220405233538.947344-1-eric.dumazet@gmail.com Signed-off-by: Jakub Kicinski

tcp_yeah: check struct yeah size at compile time

2021-06-29T18:54:36+00:00

Compiler can perform the sanity check instead of waiting to load the module and crash the host. Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller

tcp: fix stretch ACK bugs in Yeah

2020-03-17T01:26:55+00:00

Change Yeah to properly handle stretch ACKs in additive increase mode by passing in the count of ACKed packets to tcp_cong_avoid_ai(). In addition, we re-implemented the scalable path using tcp_cong_avoid_ai() and removed the pkts_acked variable. Signed-off-by: Pengcheng Yang Signed-off-by: David S. Miller

treewide: Add SPDX license identifier for more missed files

2019-05-21T08:50:45+00:00

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 Signed-off-by: Greg Kroah-Hartman

tcp: consolidate congestion control undo functions

2017-08-07T04:25:10+00:00

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 Signed-off-by: Yuchung Cheng Signed-off-by: Neal Cardwell Signed-off-by: David S. Miller

tcp: add cwnd_undo functions to various tcp cc algorithms

2016-11-21T18:20:17+00:00

congestion control algorithms that do not halve cwnd in their .ssthresh should provide a .cwnd_undo rather than rely on current fallback which assumes reno halving (and thus doubles the cwnd). All of these do 'something else' in their .ssthresh implementation, thus store the cwnd on loss and provide .undo_cwnd to restore it again. A followup patch will remove the fallback and all algorithms will need to provide a .cwnd_undo function. Signed-off-by: Florian Westphal Signed-off-by: David S. Miller

tcp: cwnd does not increase in TCP YeAH

2016-09-09T00:16:12+00:00

Commit 76174004a0f19785a328f40388e87e982bbf69b9 (tcp: do not slow start when cwnd equals ssthresh ) introduced regression in TCP YeAH. Using 100ms delay 1% loss virtual ethernet link kernel 4.2 shows bandwidth ~500KB/s for single TCP connection and kernel 4.3 and above (including 4.8-rc4) shows bandwidth ~100KB/s. That is caused by stalled cwnd when cwnd equals ssthresh. This patch fixes it by proper increasing cwnd in this case. Signed-off-by: Artem Germanov Acked-by: Dmitry Adamushko Signed-off-by: David S. Miller

tcp: replace cnt & rtt with struct in pkts_acked()

2016-05-11T18:43:19+00:00

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 Acked-by: Yuchung Cheng Signed-off-by: David S. Miller

tcp_yeah: don't set ssthresh below 2

2016-01-11T22:25:16+00:00

For tcp_yeah, use an ssthresh floor of 2, the same floor used by Reno and CUBIC, per RFC 5681 (equation 4). tcp_yeah_ssthresh() was sometimes returning a 0 or negative ssthresh value if the intended reduction is as big or bigger than the current cwnd. Congestion control modules should never return a zero or negative ssthresh. A zero ssthresh generally results in a zero cwnd, causing the connection to stall. A negative ssthresh value will be interpreted as a u32 and will set a target cwnd for PRR near 4 billion. Oleksandr Natalenko reported that a system using tcp_yeah with ECN could see a warning about a prior_cwnd of 0 in tcp_cwnd_reduction(). Testing verified that this was due to tcp_yeah_ssthresh() misbehaving in this way. Reported-by: Oleksandr Natalenko Signed-off-by: Neal Cardwell Signed-off-by: Yuchung Cheng Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller

tcp: stretch ACK fixes prep

2015-01-29T06:18:37+00:00

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 Signed-off-by: Neal Cardwell Signed-off-by: Yuchung Cheng Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller