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| author | Eric Dumazet <edumazet@google.com> | 2023-09-20 20:29:43 +0300 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2024-01-10 19:16:54 +0300 |
| commit | 030346df8cc417edbf8f8d77d152a95368480fb8 (patch) | |
| tree | 2c3b9259500b55abe6c96f425e5e6e6e49538891 /include/net | |
| parent | 88a884dec1044be5ff33fc7478586c2d870c8559 (diff) | |
| download | linux-030346df8cc417edbf8f8d77d152a95368480fb8.tar.xz | |
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 'include/net')
| -rw-r--r-- | include/net/tcp.h | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/include/net/tcp.h b/include/net/tcp.h index a88bf8f6db23..9cbcfb3c95da 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) { |