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author | Eric Dumazet <edumazet@google.com> | 2023-09-20 17:29:43 +0000 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2024-01-10 17:16:54 +0100 |
commit | 030346df8cc417edbf8f8d77d152a95368480fb8 (patch) | |
tree | 2c3b9259500b55abe6c96f425e5e6e6e49538891 /net/ipv4 | |
parent | 88a884dec1044be5ff33fc7478586c2d870c8559 (diff) | |
download | linux-stable-030346df8cc417edbf8f8d77d152a95368480fb8.tar.gz linux-stable-030346df8cc417edbf8f8d77d152a95368480fb8.tar.bz2 linux-stable-030346df8cc417edbf8f8d77d152a95368480fb8.zip |
tcp: derive delack_max from rto_min
[ 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>
Diffstat (limited to 'net/ipv4')
-rw-r--r-- | net/ipv4/tcp.c | 3 | ||||
-rw-r--r-- | net/ipv4/tcp_output.c | 16 |
2 files changed, 17 insertions, 2 deletions
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index ec46d74c2093..f124f6c63915 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 cab3c1162c3a..ab3b7b4b4429 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; |