diff mbox series

[net-next,43/44] tcp: Add mss_cache_set_by_ca for CC algorithm to set MSS

Message ID 20241015102940.26157-44-chia-yu.chang@nokia-bell-labs.com (mailing list archive)
State Changes Requested
Delegated to: Netdev Maintainers
Headers show
Series DualPI2, Accurate ECN, TCP Prague patch series | expand

Checks

Context Check Description
netdev/series_format fail Series longer than 15 patches
netdev/tree_selection success Clearly marked for net-next, async
netdev/ynl success Generated files up to date; no warnings/errors; no diff in generated;
netdev/fixes_present success Fixes tag not required for -next series
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 16 this patch: 16
netdev/build_tools success Errors and warnings before: 0 (+1) this patch: 0 (+1)
netdev/cc_maintainers fail 4 maintainers not CCed: edumazet@google.com pabeni@redhat.com dsahern@kernel.org kuba@kernel.org
netdev/build_clang success Errors and warnings before: 36 this patch: 36
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/deprecated_api success None detected
netdev/check_selftest success No net selftest shell script
netdev/verify_fixes success No Fixes tag
netdev/build_allmodconfig_warn success Errors and warnings before: 2068 this patch: 2068
netdev/checkpatch success total: 0 errors, 0 warnings, 0 checks, 32 lines checked
netdev/build_clang_rust success No Rust files in patch. Skipping build
netdev/kdoc success Errors and warnings before: 4 this patch: 4
netdev/source_inline success Was 0 now: 0

Commit Message

Chia-Yu Chang (Nokia) Oct. 15, 2024, 10:29 a.m. UTC 
From: Chia-Yu Chang <chia-yu.chang@nokia-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@nokia-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 mbox series

Patch

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);