From d050aea4cd892d71ed7fc78b6c6149a7231db5fc Mon Sep 17 00:00:00 2001 From: Dimitri Staessens Date: Sun, 5 Jul 2026 18:58:37 +0200 Subject: ipcpd: Rework congestion avoidance Congestion avoidance is a property of the layer, orthogonal to ARQ and to flow control: FRCP retransmits and lets the peer pace the sender, per flow, end-to-end; the IPCP paces path aggregates. Each signal means one thing: a loss triggers a retransmission, a mark means congestion, the peer window means a slow receiver. Every flow is paced by the same rate law whatever its QoS, so a greedy raw sender shares a bottleneck fairly with a reliable stream. The unit of control is the (destination address, QoS cube) aggregate: all flows toward that destination share one controller and one rate; a start-time fair-queuing pacer divides the rate across them by deadline instead of blocking the send path, and a new flow rides the aggregate's estimates at its current rate, with no probing of its own. Slow start runs once per aggregate. The congestion signal is a multi-bit magnitude: forwarders mark packets with their standing queue depth, MAX-combined across hops, so a packet carries the deepest queue on its path. The receiver feeds back a time-integral mean over a window that adapts to the flow's byte rate, measuring a slow flow with the same fidelity as a fast one. The sender runs AIMD scaled by elapsed wall-clock time, which makes the steady-state allocation RTT-independent. The PCI gains one byte: the path capacity as a quarter-log2 code. Forwarders estimate their egress rate from busy-period drain and MIN-stamp the byte, the receiver returns the window minimum with its feedback, and the sender scales its rate floor and additive slope to the bottleneck (C / 32). A deep cut implies a backlogged bottleneck and a backlogged bottleneck advertises its capacity, so the scaled floor is live exactly when recovery needs it: the probe heals a halving in seconds at any link rate, and the floor bounds the deepest hole to a factor 32 below the bottleneck. Signed-off-by: Dimitri Staessens Signed-off-by: Sander Vrijders --- src/lib/ssm/rbuff.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'src/lib/ssm') diff --git a/src/lib/ssm/rbuff.c b/src/lib/ssm/rbuff.c index 7886b5c2..04978d82 100644 --- a/src/lib/ssm/rbuff.c +++ b/src/lib/ssm/rbuff.c @@ -74,7 +74,7 @@ struct ssm_rbuff { ssize_t * shm_base; /* start of shared memory */ size_t * head; /* start of ringbuffer */ size_t * tail; - size_t * flags; /* out-of-band flags (RB_*) */ + size_t * flags; /* out-of-band flags (RB_*) */ pthread_mutex_t * mtx; /* lock for cond vars only */ pthread_cond_t * add; /* signal when new data */ pthread_cond_t * del; /* signal when data removed */ -- cgit v1.2.3