In the real workload, I encountered an issue which could cause the RTO
timer to retransmit the skb per 1ms with linear option enabled. The amount
of lost-retransmitted skbs can go up to 1000+ instantly.
The root cause is that if the icsk_rto happens to be zero in the 6th round
(which is the TCP_THIN_LINEAR_RETRIES value), then it will always be zero
due to the changed calculation method in tcp_retransmit_timer() as follows:
icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX);
Above line could be converted to
icsk->icsk_rto = min(0 << 1, TCP_RTO_MAX) = 0
Therefore, the timer expires so quickly without any doubt.
I read through the RFC 6298 and found that the RTO value can be rounded
up to a certain value, in Linux, say TCP_RTO_MIN as default, which is
regarded as the lower bound in this patch as suggested by Eric.
Fixes: 36e31b0af587 ("net: TCP thin linear timeouts")
Suggested-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Jason Xing <kernelxing@tencent.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Cross-merge networking fixes after downstream PR.
No conflicts.
Adjacent changes:
drivers/net/ethernet/sfc/tc.c
622ab656344a ("sfc: fix error unwinds in TC offload")
b6583d5e9e94 ("sfc: support TC decap rules matching on enc_src_port")
net/mptcp/protocol.c
5b825727d087 ("mptcp: add annotations around msk->subflow accesses")
e76c8ef5cc5b ("mptcp: refactor mptcp_stream_accept()")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
In this patch, we mainly try to handle sending a compressed ack
correctly if it's deferred.
Here are more details in the old logic:
When sack compression is triggered in the tcp_compressed_ack_kick(),
if the sock is owned by user, it will set TCP_DELACK_TIMER_DEFERRED
and then defer to the release cb phrase. Later once user releases
the sock, tcp_delack_timer_handler() should send a ack as expected,
which, however, cannot happen due to lack of ICSK_ACK_TIMER flag.
Therefore, the receiver would not sent an ack until the sender's
retransmission timeout. It definitely increases unnecessary latency.
Fixes: 5d9f4262b7ea ("tcp: add SACK compression")
Suggested-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: fuyuanli <fuyuanli@didiglobal.com>
Signed-off-by: Jason Xing <kerneljasonxing@gmail.com>
Link: https://lore.kernel.org/netdev/20230529113804.GA20300@didi-ThinkCentre-M920t-N000/
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20230531080150.GA20424@didi-ThinkCentre-M920t-N000
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Currently the SYN RTO schedule follows an exponential backoff scheme, which can be unnecessarily conservative in cases where there are link failures. In such cases, it's better to aggressively try to retransmit packets, so it takes routers less time to find a repath with a working link. We chose a default value for this sysctl of 4, to follow the macOS and IOS backoff scheme of 1,1,1,1,1,2,4,8, ... MacOS and IOS have used this backoff schedule for over a decade, since before this 2009 IETF presentation discussed the behavior: https://www.ietf.org/proceedings/75/slides/tcpm-1.pdf This commit makes the SYN RTO schedule start with a number of linear backoffs given by the following sysctl: * tcp_syn_linear_timeouts This changes the SYN RTO scheme to be: init_rto_val for tcp_syn_linear_timeouts, exp backoff starting at init_rto_val For example if init_rto_val = 1 and tcp_syn_linear_timeouts = 2, our backoff scheme would be: 1, 1, 1, 2, 4, 8, 16, ... Signed-off-by: David Morley <morleyd@google.com> Signed-off-by: Yuchung Cheng <ycheng@google.com> Signed-off-by: Neal Cardwell <ncardwell@google.com> Tested-by: David Morley <morleyd@google.com> Reviewed-by: Eric Dumazet <edumazet@google.com> Link: https://lore.kernel.org/r/20230509180558.2541885-1-morleyd.kernel@gmail.com Signed-off-by: Paolo Abeni <pabeni@redhat.com>
tcp_poll() reads sk->sk_err without socket lock held/owned. We should used READ_ONCE() here, and update writers to use WRITE_ONCE(). Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
This field can be read/written without lock synchronization. Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Instead of the hardcoded TCP_TIMEOUT_INIT, this diff calls tcp_timeout_init
to initiate req->timeout like the non TFO SYN ACK case.
Tested using the following packetdrill script, on a host with a BPF
program that sets the initial connect timeout to 10ms.
`../../common/defaults.sh`
// Initialize connection
0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+0 setsockopt(3, SOL_TCP, TCP_FASTOPEN, [1], 4) = 0
+0 bind(3, ..., ...) = 0
+0 listen(3, 1) = 0
+0 < S 0:0(0) win 32792 <mss 1000,sackOK,FO TFO_COOKIE>
+0 > S. 0:0(0) ack 1 <mss 1460,nop,nop,sackOK>
+.01 > S. 0:0(0) ack 1 <mss 1460,nop,nop,sackOK>
+.02 > S. 0:0(0) ack 1 <mss 1460,nop,nop,sackOK>
+.04 > S. 0:0(0) ack 1 <mss 1460,nop,nop,sackOK>
+.01 < . 1:1(0) ack 1 win 32792
+0 accept(3, ..., ...) = 4
Signed-off-by: Jie Meng <jmeng@fb.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Acked-by: Yuchung Cheng <ycheng@google.com>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
No conflicts. Signed-off-by: Jakub Kicinski <kuba@kernel.org>
While reading sysctl_tcp_thin_linear_timeouts, it can be changed
concurrently. Thus, we need to add READ_ONCE() to its reader.
Fixes: 36e31b0af587 ("net: TCP thin linear timeouts")
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
While reading these sysctl knobs, they can be changed concurrently.
Thus, we need to add READ_ONCE() to their readers.
- tcp_retries1
- tcp_retries2
- tcp_orphan_retries
- tcp_fin_timeout
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>