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 <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>
Signed-off-by: Juhyung Park <qkrwngud825@gmail.com>
In order to track CE marks per rate sample (one round trip), TCP needs a
per-skb header field to record the tp->delivered_ce count when the skb
was sent. To make space, we replace the "last_in_flight" field which is
used exclusively for NV congestion control. The stat needed by NV can be
alternatively approximated by existing stats tcp_sock delivered and
mss_cache.
This patch counts the number of packets delivered which have CE marks in
the rate sample, using similar approach of delivery accounting.
Cc: Lawrence Brakmo <brakmo@fb.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Luke Hsiao <lukehsiao@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Juhyung Park <qkrwngud825@gmail.com>
When we fragment an skb that has already been sent, we need to update
the tx.in_flight for the first skb in the resulting pair ("buff").
Because we were not updating the tx.in_flight, the tx.in_flight value
was inconsistent with the pcount of the "buff" skb (tx.in_flight would
be too high). That meant that if the "buff" skb was lost, then
bbr2_inflight_hi_from_lost_skb() would calculate an inflight_hi value
that is too high. This could result in longer queues and higher packet
loss.
Packetdrill testing verified that without this commit, when the second
half of an skb is SACKed and then later the first half of that skb is
marked lost, the calculated inflight_hi was incorrect.
Effort: net-tcp_bbr
Origin-9xx-SHA1: 385f1ddc610798fab2837f9f372857438b25f874
Origin-9xx-SHA1: a0eb099690af net-tcp_bbr: v2: fix tcp_fragment() tx.in_flight recomputation [prod feb 8 2021; use as a fixup]
Origin-9xx-SHA1: 885503228153ff0c9114e net-tcp_bbr: v2: introduce tcp_skb_tx_in_flight_is_suspicious() helper for warnings
Change-Id: I617f8cab4e9be7a0b8e8d30b047bf8645393354d
Signed-off-by: Juhyung Park <qkrwngud825@gmail.com>
Define and implement a new per-route feature, RTAX_FEATURE_ECN_LOW.
This feature indicates that the given destination network is a
low-latency ECN environment, meaning both that ECN CE marks are
applied by the network using a low-latency marking threshold and also
that TCP endpoints provide precise per-data-segment ECN feedback in
ACKs (where the ACK ECE flag echoes the received CE status of all
newly-acknowledged data segments). This feature indication can be used
by congestion control algorithms to decide how to interpret ECN
signals over the given destination network.
This feature is appropriate for datacenter-style ECN marking, such as
the ECN marking approach expected by DCTCP or BBR congestion control
modules.
Signed-off-by: David Morley <morleyd@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Tested-by: David Morley <morleyd@google.com>
Change-Id: I6bc06e9c6cb426fbae7243fc71c9a8c18175f5d3
Signed-off-by: Juhyung Park <qkrwngud825@gmail.com>
[ Upstream commit eb44ad4e635132754bfbcb18103f1dcb7058aedd ]
This field can be read or written without socket lock being held.
Add annotations to avoid load-store tearing.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
commit f921a4a5bffa8a0005b190fb9421a7fc1fd716b6 upstream.
In commit 75eefc6c59fd ("tcp: tsq: add a shortcut in tcp_small_queue_check()")
we allowed to send an skb regardless of TSQ limits being hit if rtx queue
was empty or had a single skb, in order to better fill the pipe
when/if TX completions were slow.
Then later, commit 75c119afe14f ("tcp: implement rb-tree based
retransmit queue") accidentally removed the special case for
one skb in rtx queue.
Stefan Wahren reported a regression in single TCP flow throughput
using a 100Mbit fec link, starting from commit 65466904b015 ("tcp: adjust
TSO packet sizes based on min_rtt"). This last commit only made the
regression more visible, because it locked the TCP flow on a particular
behavior where TSQ prevented two skbs being pushed downstream,
adding silences on the wire between each TSO packet.
Many thanks to Stefan for his invaluable help !
Fixes: 75c119afe14f ("tcp: implement rb-tree based retransmit queue")
Link: https://lore.kernel.org/netdev/7f31ddc8-9971-495e-a1f6-819df542e0af@gmx.net/
Reported-by: Stefan Wahren <wahrenst@gmx.net>
Tested-by: Stefan Wahren <wahrenst@gmx.net>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Link: https://lore.kernel.org/r/20231017124526.4060202-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
commit 1c2709cfff1dedbb9591e989e2f001484208d914 upstream.
We discovered from packet traces of slow loss recovery on kernels with
the default HZ=250 setting (and min_rtt < 1ms) that after reordering,
when receiving a SACKed sequence range, the RACK reordering timer was
firing after about 16ms rather than the desired value of roughly
min_rtt/4 + 2ms. The problem is largely due to the RACK reorder timer
calculation adding in TCP_TIMEOUT_MIN, which is 2 jiffies. On kernels
with HZ=250, this is 2*4ms = 8ms. The TLP timer calculation has the
exact same issue.
This commit fixes the TLP transmit timer and RACK reordering timer
floor calculation to more closely match the intended 2ms floor even on
kernels with HZ=250. It does this by adding in a new
TCP_TIMEOUT_MIN_US floor of 2000 us and then converting to jiffies,
instead of the current approach of converting to jiffies and then
adding th TCP_TIMEOUT_MIN value of 2 jiffies.
Our testing has verified that on kernels with HZ=1000, as expected,
this does not produce significant changes in behavior, but on kernels
with the default HZ=250 the latency improvement can be large. For
example, our tests show that for HZ=250 kernels at low RTTs this fix
roughly halves the latency for the RACK reorder timer: instead of
mostly firing at 16ms it mostly fires at 8ms.
Suggested-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Fixes: bb4d991a28cc ("tcp: adjust tail loss probe timeout")
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20231015174700.2206872-1-ncardwell.sw@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
