tcp: add sysctls for TCP PLB parameters

PLB (Protective Load Balancing) is a host based mechanism for load
balancing across switch links. It leverages congestion signals(e.g. ECN)
from transport layer to randomly change the path of the connection
experiencing congestion. PLB changes the path of the connection by
changing the outgoing IPv6 flow label for IPv6 connections (implemented
in Linux by calling sk_rethink_txhash()). Because of this implementation
mechanism, PLB can currently only work for IPv6 traffic. For more
information, see the SIGCOMM 2022 paper:
  https://doi.org/10.1145/3544216.3544226

This commit adds new sysctl knobs and sets their default values for
TCP PLB.

Signed-off-by: Mubashir Adnan Qureshi <mubashirq@google.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 43 insertions, 0 deletions

diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index 9b8a6db7a66b..0af28cedd071 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -40,6 +40,8 @@ static int one_day_secs = 24 * 3600;
 static u32 fib_multipath_hash_fields_all_mask __maybe_unused =
 	FIB_MULTIPATH_HASH_FIELD_ALL_MASK;
 static unsigned int tcp_child_ehash_entries_max = 16 * 1024 * 1024;
+static int tcp_plb_max_rounds = 31;
+static int tcp_plb_max_cong_thresh = 256;
 
 /* obsolete */
 static int sysctl_tcp_low_latency __read_mostly;
@@ -1384,6 +1386,47 @@ static struct ctl_table ipv4_net_table[] = {
 		.extra1		= SYSCTL_ZERO,
 		.extra2		= SYSCTL_TWO,
 	},
+	{
+		.procname       = "tcp_plb_enabled",
+		.data           = &init_net.ipv4.sysctl_tcp_plb_enabled,
+		.maxlen         = sizeof(u8),
+		.mode           = 0644,
+		.proc_handler   = proc_dou8vec_minmax,
+		.extra1         = SYSCTL_ZERO,
+		.extra2         = SYSCTL_ONE,
+	},
+	{
+		.procname       = "tcp_plb_idle_rehash_rounds",
+		.data           = &init_net.ipv4.sysctl_tcp_plb_idle_rehash_rounds,
+		.maxlen         = sizeof(u8),
+		.mode           = 0644,
+		.proc_handler   = proc_dou8vec_minmax,
+		.extra2		= &tcp_plb_max_rounds,
+	},
+	{
+		.procname       = "tcp_plb_rehash_rounds",
+		.data           = &init_net.ipv4.sysctl_tcp_plb_rehash_rounds,
+		.maxlen         = sizeof(u8),
+		.mode           = 0644,
+		.proc_handler   = proc_dou8vec_minmax,
+		.extra2         = &tcp_plb_max_rounds,
+	},
+	{
+		.procname       = "tcp_plb_suspend_rto_sec",
+		.data           = &init_net.ipv4.sysctl_tcp_plb_suspend_rto_sec,
+		.maxlen         = sizeof(u8),
+		.mode           = 0644,
+		.proc_handler   = proc_dou8vec_minmax,
+	},
+	{
+		.procname       = "tcp_plb_cong_thresh",
+		.data           = &init_net.ipv4.sysctl_tcp_plb_cong_thresh,
+		.maxlen         = sizeof(int),
+		.mode           = 0644,
+		.proc_handler   = proc_dointvec_minmax,
+		.extra1         = SYSCTL_ZERO,
+		.extra2         = &tcp_plb_max_cong_thresh,
+	},
 	{ }
 };