From 537b1b761e1d0036923adba7a80d3655cfff095d Mon Sep 17 00:00:00 2001 From: David Morley Date: Fri, 21 Jul 2023 09:20:46 +0000 Subject: [PATCH 1/2] ip: introduce the ecn_low per-route feature Add a a new "ecn_low" feature that administrators can add to a particular ip route. The ecn_low feature indicates that the given destination network is a low-latency ECN environment, meaning both that ECN CE marks are applied by the network using a low-latency marking threshold and also that TCP endpoints provide precise per-data-segment ECN feedback in ACKs (where the ACK ECE flag echoes the received CE status of all newly-acknowledged data segments). This ecn_low feature indication can be used by congestion control algorithms to decide how to interpret ECN signals over the given destination network. Signed-off-by: David Morley Signed-off-by: Neal Cardwell --- include/uapi/linux/rtnetlink.h | 4 +++- ip/iproute.c | 8 +++++++- man/man8/ip-route.8.in | 19 ++++++++++++++----- 3 files changed, 24 insertions(+), 7 deletions(-) --- a/include/uapi/linux/rtnetlink.h +++ b/include/uapi/linux/rtnetlink.h @@ -508,12 +508,14 @@ enum { #define RTAX_FEATURE_TIMESTAMP (1 << 2) /* unused */ #define RTAX_FEATURE_ALLFRAG (1 << 3) /* unused */ #define RTAX_FEATURE_TCP_USEC_TS (1 << 4) +#define RTAX_FEATURE_ECN_LOW (1 << 5) #define RTAX_FEATURE_MASK (RTAX_FEATURE_ECN | \ RTAX_FEATURE_SACK | \ RTAX_FEATURE_TIMESTAMP | \ RTAX_FEATURE_ALLFRAG | \ - RTAX_FEATURE_TCP_USEC_TS) + RTAX_FEATURE_TCP_USEC_TS | \ + RTAX_FEATURE_ECN_LOW) struct rta_session { __u8 proto; --- a/ip/iproute.c +++ b/ip/iproute.c @@ -97,7 +97,7 @@ static void usage(void) "PREF := [ low | medium | high ]\n" "TIME := NUMBER[s|ms]\n" "BOOL := [1|0]\n" - "FEATURES := ecn\n" + "FEATURES := [ ecn | ecn_low ]\n" "ENCAPTYPE := [ mpls | ip | ip6 | seg6 | seg6local | rpl | ioam6 | xfrm ]\n" "ENCAPHDR := [ MPLSLABEL | SEG6HDR | SEG6LOCAL | IOAM6HDR | XFRMINFO ]\n" "SEG6HDR := [ mode SEGMODE ] segs ADDR1,ADDRi,ADDRn [hmac HMACKEYID] [cleanup]\n" @@ -373,6 +373,10 @@ static void print_rtax_features(FILE *fp print_null(PRINT_ANY, "ecn", "ecn ", NULL); features &= ~RTAX_FEATURE_ECN; } + if (features & RTAX_FEATURE_ECN_LOW) { + print_null(PRINT_ANY, "ecn_low", "ecn_low ", NULL); + features &= ~RTAX_FEATURE_ECN_LOW; + } if (features & RTAX_FEATURE_TCP_USEC_TS) { print_null(PRINT_ANY, "tcp_usec_ts", "tcp_usec_ts ", NULL); @@ -1381,6 +1385,8 @@ static int iproute_modify(int cmd, unsig features |= RTAX_FEATURE_ECN; else if (strcmp(*argv, "tcp_usec_ts") == 0) features |= RTAX_FEATURE_TCP_USEC_TS; + else if (strcmp(*argv, "ecn_low") == 0) + features |= RTAX_FEATURE_ECN_LOW; else invarg("\"features\" value not valid\n", *argv); break; --- a/man/man8/ip-route.8.in +++ b/man/man8/ip-route.8.in @@ -184,7 +184,7 @@ throw " | " unreachable " | " prohibit " .ti -8 .IR FEATURES " := [ " -.BR ecn " | ]" +.BR ecn " | " ecn_low " ] " .ti -8 .IR PREF " := [ " @@ -556,16 +556,25 @@ The default value is zero, meaning to us .TP .BI features " FEATURES " (Linux 3.18+ only) -Enable or disable per-route features. Only available feature at this -time is -.B ecn -to enable explicit congestion notification when initiating connections to the +Enable or disable per-route features. Available features include: + +.BI ecn +- to enable explicit congestion notification when initiating connections to the given destination network. When responding to a connection request from the given network, ecn will also be used even if the .B net.ipv4.tcp_ecn sysctl is set to 0. +.BI ecn_low +- to indicate that the given destination network is a low-latency ECN +environment, meaning both that ECN CE marks are applied by the network using a +low-latency marking threshold and also that TCP endpoints provide precise +per-data-segment ECN feedback in ACKs (where the ACK ECE flag echoes the +received CE status of all newly-acknowledged data segments). This ecn_low +feature indication can be used by congestion control algorithms to decide how +to interpret ECN signals over the given destination network (Linux 6.7+ only). + .TP .BI quickack " BOOL " "(Linux 3.11+ only)" Enable or disable quick ack for connections to this destination.