From 3388bd9e9b82df6d7fe79fa4eee7c22a3277624e Mon Sep 17 00:00:00 2001 From: Dimitri Staessens Date: Tue, 21 Jul 2026 06:54:55 +0200 Subject: ipcpd: Add flow overshoot protection to mb-ecn The ECN marks were the only source of congestion information, and going into congestion collapse (dropping a lot of ECN packets and causing loss of signal) was unrecoverable. The sender's slow-start ramp clock now tracks a measured RTT to avoid overshooting into congestion collapse on the previously fixed (14ms) doubling on long-delay (e.g. 100ms) links. The flow allocator now carries a periodic heartbeat/ack to keep RTT estimates up-to-date. The heartbeat also serves as a congestion collapse detector: consecutive heartbeat losses will go into loss recovery, halving the window and pausing Additive Increase until the path is clear. The DT component now has a max_rtt config parameter that serves as a hint for the layer RTT to optimize slow-start for low-latency networks. These two mechanisms follow TCP, however only during slow start up to the first ECN signal and to recover from a total collapse until the ECN signal returns. MB-ECN is still fully RTT-independent in the AI/PD region. A shorter RTT path will just reach its equal fair share faster than a longer RTT path. Signed-off-by: Dimitri Staessens Signed-off-by: Sander Vrijders --- src/ipcpd/unicast/ca/mb-ecn.h | 9 +++++++++ 1 file changed, 9 insertions(+) (limited to 'src/ipcpd/unicast/ca/mb-ecn.h') diff --git a/src/ipcpd/unicast/ca/mb-ecn.h b/src/ipcpd/unicast/ca/mb-ecn.h index 7bf0b29f..781e25a8 100644 --- a/src/ipcpd/unicast/ca/mb-ecn.h +++ b/src/ipcpd/unicast/ca/mb-ecn.h @@ -25,6 +25,8 @@ #include "ops.h" +void mb_ecn_init(uint32_t rtt_ms); + void * mb_ecn_ctx_create(void); void mb_ecn_ctx_destroy(void * ctx); @@ -45,6 +47,13 @@ void mb_ecn_ctx_update_ece(void * ctx, uint16_t ece, uint8_t cap); +bool mb_ecn_ctx_hb_due(void * ctx, + uint64_t now); + +void mb_ecn_ctx_rtt(void * ctx, + uint64_t now, + uint64_t rtt); + int mb_ecn_calc_ecn(size_t queued, uint8_t * ecn, qoscube_t qc, -- cgit v1.2.3