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/ops.h | 8 ++++++++ 1 file changed, 8 insertions(+) (limited to 'src/ipcpd/unicast/ca/ops.h') diff --git a/src/ipcpd/unicast/ca/ops.h b/src/ipcpd/unicast/ca/ops.h index a86c1b3b..b01e8573 100644 --- a/src/ipcpd/unicast/ca/ops.h +++ b/src/ipcpd/unicast/ca/ops.h @@ -46,6 +46,14 @@ struct ca_ops { uint16_t ece, uint8_t cap); + /* Optional, can be NULL: heartbeat pacing + RTT feedback. */ + bool (* ctx_hb_due)(void * ctx, + uint64_t now); + + void (* ctx_rtt)(void * ctx, + uint64_t now, + uint64_t rtt); + int (* calc_ecn)(size_t queued, uint8_t * ecn, qoscube_t qc, -- cgit v1.2.3