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tcp: reduce tcp_comp_sack_slack_ns default value to 10 usec

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net.ipv4.tcp_comp_sack_slack_ns current default value is too high.

When a flow has many drops (1 % or more), and small RTT, adding 100 usec
before sending SACK stalls the sender relying on getting SACK
fast enough to keep the pipe busy.

Decrease the default to 10 usec.

This is orthogonal to Congestion Control heuristics to determine
if drops are caused by congestion or not.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Neal Cardwell <ncardwell@google.com>
Link: https://patch.msgid.link/20251114135141.3810964-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Eric Dumazet
2025-11-14 13:51:41 +00:00
committed by Jakub Kicinski
parent 5860bb1ce0
commit ca412f25d6
2 changed files with 3 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files

3
Documentation/networking/ip-sysctl.rst
View File

@@ -875,8 +875,9 @@ tcp_comp_sack_slack_ns - LONG INTEGER
timer used by SACK compression. This gives extra time
for small RTT flows, and reduces system overhead by allowing
opportunistic reduction of timer interrupts.
Too big values might reduce goodput.
Default : 100,000 ns (100 us)
Default : 10,000 ns (10 us)
tcp_comp_sack_nr - INTEGER
Max number of SACK that can be compressed.

2
net/ipv4/tcp_ipv4.c
View File

@@ -3593,7 +3593,7 @@ static int __net_init tcp_sk_init(struct net *net)
sizeof(init_net.ipv4.sysctl_tcp_wmem));
}
net->ipv4.sysctl_tcp_comp_sack_delay_ns = NSEC_PER_MSEC;
net->ipv4.sysctl_tcp_comp_sack_slack_ns = 100 * NSEC_PER_USEC;
net->ipv4.sysctl_tcp_comp_sack_slack_ns = 10 * NSEC_PER_USEC;
net->ipv4.sysctl_tcp_comp_sack_nr = 44;
net->ipv4.sysctl_tcp_comp_sack_rtt_percent = 33;
net->ipv4.sysctl_tcp_backlog_ack_defer = 1;