Add a delta parameter to Vegas.

This allows us to cap the queue use during steady state. In shadow, this
reduced instances of long circuit queues at relays.

2 files changed, 28 insertions, 2 deletions

diff --git a/src/core/or/congestion_control_st.h b/src/core/or/congestion_control_st.h
index ea80868350..2c905772c1 100644
--- a/src/core/or/congestion_control_st.h
+++ b/src/core/or/congestion_control_st.h
@@ -103,6 +103,8 @@ struct vegas_params_t {
     uint16_t alpha;
     /** The queue use above which we decrement cwnd */
     uint16_t beta;
+    /** The queue use at which we cap cwnd in steady state */
+    uint16_t delta;
     /** Weighted average (percent) between cwnd estimator and
      * piecewise estimator. */
     uint8_t bdp_mix_pct;
diff --git a/src/core/or/congestion_control_vegas.c b/src/core/or/congestion_control_vegas.c
index ff825f94cc..5c62787375 100644
--- a/src/core/or/congestion_control_vegas.c
+++ b/src/core/or/congestion_control_vegas.c
@@ -29,27 +29,32 @@
 #define VEGAS_ALPHA_SBWS_DFLT (2*OUTBUF_CELLS-TLS_RECORD_MAX_CELLS)
 #define VEGAS_BETA_SBWS_DFLT (2*OUTBUF_CELLS)
 #define VEGAS_GAMMA_SBWS_DFLT (2*OUTBUF_CELLS)
+#define VEGAS_DELTA_SBWS_DFLT (4*OUTBUF_CELLS)
 
 /* Exits are three hops, so params are based on 3 outbufs of cells */
 #define VEGAS_ALPHA_EXIT_DFLT (3*OUTBUF_CELLS-TLS_RECORD_MAX_CELLS)
 #define VEGAS_BETA_EXIT_DFLT (3*OUTBUF_CELLS)
 #define VEGAS_GAMMA_EXIT_DFLT (3*OUTBUF_CELLS)
+#define VEGAS_DELTA_EXIT_DFLT (5*OUTBUF_CELLS)
 
 /* Onion rends are six hops, so params are based on 6 outbufs of cells */
 #define VEGAS_ALPHA_ONION_DFLT (6*OUTBUF_CELLS-TLS_RECORD_MAX_CELLS)
 #define VEGAS_BETA_ONION_DFLT (6*OUTBUF_CELLS)
 #define VEGAS_GAMMA_ONION_DFLT (6*OUTBUF_CELLS)
+#define VEGAS_DELTA_ONION_DFLT (8*OUTBUF_CELLS)
 
 /* Single Onions are three hops, so params are based on 3 outbufs of cells */
 #define VEGAS_ALPHA_SOS_DFLT (3*OUTBUF_CELLS-TLS_RECORD_MAX_CELLS)
 #define VEGAS_BETA_SOS_DFLT (3*OUTBUF_CELLS)
 #define VEGAS_GAMMA_SOS_DFLT (3*OUTBUF_CELLS)
+#define VEGAS_DELTA_SOS_DFLT (5*OUTBUF_CELLS)
 
 /* Vanguard Onions are 7 hops (or 8 if both sides use vanguards, but that
  * should be rare), so params are based on 7 outbufs of cells */
 #define VEGAS_ALPHA_VG_DFLT (7*OUTBUF_CELLS-TLS_RECORD_MAX_CELLS)
 #define VEGAS_BETA_VG_DFLT (7*OUTBUF_CELLS)
 #define VEGAS_GAMMA_VG_DFLT (7*OUTBUF_CELLS)
+#define VEGAS_DELTA_VG_DFLT (9*OUTBUF_CELLS)
 
 #define VEGAS_BDP_MIX_PCT       100
 
@@ -81,48 +86,59 @@ congestion_control_vegas_set_params(congestion_control_t *cc,
 {
   tor_assert(cc->cc_alg == CC_ALG_VEGAS);
   const char *alpha_str = NULL, *beta_str = NULL, *gamma_str = NULL;
-  int alpha, beta, gamma;
+  const char *delta_str = NULL;
+  int alpha, beta, gamma, delta;
 
   switch (path) {
     case CC_PATH_SBWS:
       alpha_str = "cc_vegas_alpha_sbws";
       beta_str = "cc_vegas_beta_sbws";
       gamma_str = "cc_vegas_gamma_sbws";
+      delta_str = "cc_vegas_delta_sbws";
       alpha = VEGAS_ALPHA_SBWS_DFLT;
       beta = VEGAS_BETA_SBWS_DFLT;
       gamma = VEGAS_GAMMA_SBWS_DFLT;
+      delta = VEGAS_DELTA_SBWS_DFLT;
       break;
     case CC_PATH_EXIT:
       alpha_str = "cc_vegas_alpha_exit";
       beta_str = "cc_vegas_beta_exit";
       gamma_str = "cc_vegas_gamma_exit";
+      delta_str = "cc_vegas_delta_exit";
       alpha = VEGAS_ALPHA_EXIT_DFLT;
       beta = VEGAS_BETA_EXIT_DFLT;
       gamma = VEGAS_GAMMA_EXIT_DFLT;
+      delta = VEGAS_DELTA_EXIT_DFLT;
       break;
     case CC_PATH_ONION:
       alpha_str = "cc_vegas_alpha_onion";
       beta_str = "cc_vegas_beta_onion";
       gamma_str = "cc_vegas_gamma_onion";
+      delta_str = "cc_vegas_delta_onion";
       alpha = VEGAS_ALPHA_ONION_DFLT;
       beta = VEGAS_BETA_ONION_DFLT;
       gamma = VEGAS_GAMMA_ONION_DFLT;
+      delta = VEGAS_DELTA_ONION_DFLT;
       break;
     case CC_PATH_ONION_SOS:
       alpha_str = "cc_vegas_alpha_sos";
       beta_str = "cc_vegas_beta_sos";
       gamma_str = "cc_vegas_gamma_sos";
+      delta_str = "cc_vegas_delta_sos";
       alpha = VEGAS_ALPHA_SOS_DFLT;
       beta = VEGAS_BETA_SOS_DFLT;
       gamma = VEGAS_GAMMA_SOS_DFLT;
+      delta = VEGAS_DELTA_SOS_DFLT;
       break;
     case CC_PATH_ONION_VG:
       alpha_str = "cc_vegas_alpha_vg";
       beta_str = "cc_vegas_beta_vg";
       gamma_str = "cc_vegas_gamma_vg";
+      delta_str = "cc_vegas_delta_vg";
       alpha = VEGAS_ALPHA_VG_DFLT;
       beta = VEGAS_BETA_VG_DFLT;
       gamma = VEGAS_GAMMA_VG_DFLT;
+      delta = VEGAS_DELTA_VG_DFLT;
       break;
     default:
       tor_assert(0);
@@ -147,6 +163,12 @@ congestion_control_vegas_set_params(congestion_control_t *cc,
       0,
       1000);
 
+  cc->vegas_params.delta =
+   networkstatus_get_param(NULL, delta_str,
+      delta,
+      0,
+      INT32_MAX);
+
   cc->vegas_params.bdp_mix_pct =
    networkstatus_get_param(NULL, "cc_vegas_bdp_mix",
       VEGAS_BDP_MIX_PCT,
@@ -216,7 +238,9 @@ congestion_control_vegas_process_sendme(congestion_control_t *cc,
         log_info(LD_CIRC, "CC: TOR_VEGAS exiting slow start");
       }
     } else {
-      if (queue_use > cc->vegas_params.beta || cc->blocked_chan) {
+      if (queue_use > cc->vegas_params.delta) {
+        cc->cwnd = vegas_bdp_mix(cc) + cc->vegas_params.delta - CWND_INC(cc);
+      } else if (queue_use > cc->vegas_params.beta || cc->blocked_chan) {
         cc->cwnd -= CWND_INC(cc);
       } else if (queue_use < cc->vegas_params.alpha) {
         cc->cwnd += CWND_INC(cc);