revert a751264, hard-coding beta exitting slow start to 0.5 (because …

…loss signal arrives 1 rtt later and slow start is 2x per rtt)
h2o · Nov 6, 2023 · 21d2975 · 21d2975
1 parent 857382d
commit 21d2975
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Showing 2 changed files with 4 additions and 2 deletions.
diff --git a/include/quicly/cc.h b/include/quicly/cc.h
@@ -38,7 +38,7 @@ extern "C" {
 #include "quicly/loss.h"
 
 #define QUICLY_MIN_CWND 2
-#define QUICLY_RENO_BETA 0.5
+#define QUICLY_RENO_BETA 0.7
 
 /**
  * Holds pointers to concrete congestion control implementation functions.

diff --git a/lib/cc-reno.c b/lib/cc-reno.c
@@ -58,7 +58,9 @@ static void reno_on_acked(quicly_cc_t *cc, const quicly_loss_t *loss, uint32_t b
 void quicly_cc_reno_on_lost(quicly_cc_t *cc, const quicly_loss_t *loss, uint32_t bytes, uint64_t lost_pn, uint64_t next_pn,
                             int64_t now, uint32_t max_udp_payload_size)
 {
-    double beta = QUICLY_RENO_BETA;
+    /* when exiting slow start, use inverse of exponential growth ratio, as loss is detected 1 RTT later, at which point CWND has
+     * overshot as much as the growth ratio */
+    double beta = cc->ssthresh == UINT32_MAX ? 0.5 : QUICLY_RENO_BETA;
 
     quicly_cc__update_ecn_episodes(cc, bytes, lost_pn);