netdev - [PATCH net-next 43/44] tcp: Add mss_cache_set_by

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20241015102940.26157-44-chia-yu.chang@nokia-bell-labs.com>
Date: Tue, 15 Oct 2024 12:29:39 +0200
From: chia-yu.chang@...ia-bell-labs.com
To: netdev@...r.kernel.org, ij@...nel.org, ncardwell@...gle.com,
        koen.de_schepper@...ia-bell-labs.com, g.white@...leLabs.com,
        ingemar.s.johansson@...csson.com, mirja.kuehlewind@...csson.com,
        cheshire@...le.com, rs.ietf@....at, Jason_Livingood@...cast.com,
        vidhi_goel@...le.com
Cc: Chia-Yu Chang <chia-yu.chang@...ia-bell-labs.com>
Subject: [PATCH net-next 43/44] tcp: Add mss_cache_set_by_ca for CC algorithm to set MSS

From: Chia-Yu Chang <chia-yu.chang@...ia-bell-labs.com>

Make the CC module set the mss_cache smaller than path mtu. This is useful
for a CC module that maintains an internal fractional cwnd less than 2 at
very low speed (<100kbps) and very low RTT (<1ms). In this case, the
minimum snd_cwnd for the stack remains at 2, but the CC module will limit
the pacing rate to ensure that its internal fractional cwnd takes effect.
Therefore, the CC algorithm can enable fine-grained control without
causing big rate saw-tooth and delay jitter.

Signed-off-by: Chia-Yu Chang <chia-yu.chang@...ia-bell-labs.com>
---
 include/linux/tcp.h   | 3 ++-
 net/ipv4/tcp.c        | 1 +
 net/ipv4/tcp_output.c | 4 ++--
 3 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index ecc9cfa7210f..add0da4dbedc 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -232,7 +232,8 @@ struct tcp_sock {
 		repair      : 1,
 		tcp_usec_ts : 1, /* TSval values in usec */
 		is_sack_reneg:1,    /* in recovery from loss with SACK reneg? */
-		is_cwnd_limited:1;/* forward progress limited by snd_cwnd? */
+		is_cwnd_limited:1,/* forward progress limited by snd_cwnd? */
+		mss_cache_set_by_ca:1;/* mss_cache set by CA */
 	__cacheline_group_end(tcp_sock_read_txrx);
 
 	/* RX read-mostly hotpath cache lines */
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 16bf550a619b..13db4db1be55 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -456,6 +456,7 @@ void tcp_init_sock(struct sock *sk)
 	tp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
 	tp->snd_cwnd_clamp = ~0;
 	tp->mss_cache = TCP_MSS_DEFAULT;
+	tp->mss_cache_set_by_ca = false;
 
 	tp->reordering = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_reordering);
 	tcp_assign_congestion_control(sk);
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 0f0e79b42941..d84c3897e932 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2074,7 +2074,7 @@ unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu)
 	struct inet_connection_sock *icsk = inet_csk(sk);
 	int mss_now;
 
-	if (icsk->icsk_mtup.search_high > pmtu)
+	if (icsk->icsk_mtup.search_high > pmtu && !tp->mss_cache_set_by_ca)
 		icsk->icsk_mtup.search_high = pmtu;
 
 	mss_now = tcp_mtu_to_mss(sk, pmtu);
@@ -2104,7 +2104,7 @@ unsigned int tcp_current_mss(struct sock *sk)
 
 	mss_now = tp->mss_cache;
 
-	if (dst) {
+	if (dst && !tp->mss_cache_set_by_ca) {
 		u32 mtu = dst_mtu(dst);
 		if (mtu != inet_csk(sk)->icsk_pmtu_cookie)
 			mss_now = tcp_sync_mss(sk, mtu);
-- 
2.34.1