6.6-stable review patch. If anyone has any objections, please let me know.
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From: Eric Dumazet edumazet@google.com
[ Upstream commit bbf80d713fe75cfbecda26e7c03a9a8d22af2f4f ]
While BPF allows to set icsk->->icsk_delack_max and/or icsk->icsk_rto_min, we have an ip route attribute (RTAX_RTO_MIN) to be able to tune rto_min, but nothing to consequently adjust max delayed ack, which vary from 40ms to 200 ms (TCP_DELACK_{MIN|MAX}).
This makes RTAX_RTO_MIN of almost no practical use, unless customers are in big trouble.
Modern days datacenter communications want to set rto_min to ~5 ms, and the max delayed ack one jiffie smaller to avoid spurious retransmits.
After this patch, an "rto_min 5" route attribute will effectively lower max delayed ack timers to 4 ms.
Note in the following ss output, "rto:6 ... ato:4"
$ ss -temoi dst XXXXXX State Recv-Q Send-Q Local Address:Port Peer Address:Port Process ESTAB 0 0 [2002:a05:6608:295::]:52950 [2002:a05:6608:297::]:41597 ino:255134 sk:1001 <-> skmem:(r0,rb1707063,t872,tb262144,f0,w0,o0,bl0,d0) ts sack cubic wscale:8,8 rto:6 rtt:0.02/0.002 ato:4 mss:4096 pmtu:4500 rcvmss:536 advmss:4096 cwnd:10 bytes_sent:54823160 bytes_acked:54823121 bytes_received:54823120 segs_out:1370582 segs_in:1370580 data_segs_out:1370579 data_segs_in:1370578 send 16.4Gbps pacing_rate 32.6Gbps delivery_rate 1.72Gbps delivered:1370579 busy:26920ms unacked:1 rcv_rtt:34.615 rcv_space:65920 rcv_ssthresh:65535 minrtt:0.015 snd_wnd:65536
While we could argue this patch fixes a bug with RTAX_RTO_MIN, I do not add a Fixes: tag, so that we can soak it a bit before asking backports to stable branches.
Signed-off-by: Eric Dumazet edumazet@google.com Acked-by: Soheil Hassas Yeganeh soheil@google.com Acked-by: Neal Cardwell ncardwell@google.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Sasha Levin sashal@kernel.org --- include/net/tcp.h | 2 ++ net/ipv4/tcp.c | 3 ++- net/ipv4/tcp_output.c | 16 +++++++++++++++- 3 files changed, 19 insertions(+), 2 deletions(-)
diff --git a/include/net/tcp.h b/include/net/tcp.h index a88bf8f6db235..9cbcfb3c95dac 100644 --- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -723,6 +723,8 @@ static inline void tcp_fast_path_check(struct sock *sk) tcp_fast_path_on(tp); }
+u32 tcp_delack_max(const struct sock *sk); + /* Compute the actual rto_min value */ static inline u32 tcp_rto_min(struct sock *sk) { diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index ec46d74c20938..f124f6c639157 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -3774,7 +3774,8 @@ void tcp_get_info(struct sock *sk, struct tcp_info *info) info->tcpi_options |= TCPI_OPT_SYN_DATA;
info->tcpi_rto = jiffies_to_usecs(icsk->icsk_rto); - info->tcpi_ato = jiffies_to_usecs(icsk->icsk_ack.ato); + info->tcpi_ato = jiffies_to_usecs(min(icsk->icsk_ack.ato, + tcp_delack_max(sk))); info->tcpi_snd_mss = tp->mss_cache; info->tcpi_rcv_mss = icsk->icsk_ack.rcv_mss;
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index cab3c1162c3a6..ab3b7b4b4429b 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -4003,6 +4003,20 @@ int tcp_connect(struct sock *sk) } EXPORT_SYMBOL(tcp_connect);
+u32 tcp_delack_max(const struct sock *sk) +{ + const struct dst_entry *dst = __sk_dst_get(sk); + u32 delack_max = inet_csk(sk)->icsk_delack_max; + + if (dst && dst_metric_locked(dst, RTAX_RTO_MIN)) { + u32 rto_min = dst_metric_rtt(dst, RTAX_RTO_MIN); + u32 delack_from_rto_min = max_t(int, 1, rto_min - 1); + + delack_max = min_t(u32, delack_max, delack_from_rto_min); + } + return delack_max; +} + /* Send out a delayed ack, the caller does the policy checking * to see if we should even be here. See tcp_input.c:tcp_ack_snd_check() * for details. @@ -4038,7 +4052,7 @@ void tcp_send_delayed_ack(struct sock *sk) ato = min(ato, max_ato); }
- ato = min_t(u32, ato, inet_csk(sk)->icsk_delack_max); + ato = min_t(u32, ato, tcp_delack_max(sk));
/* Stay within the limit we were given */ timeout = jiffies + ato;