TOR_VEGAS: Implement Prop#324 TOR_VEGAS.

2 files changed, 233 insertions, 0 deletions

diff --git a/src/core/or/congestion_control_vegas.c b/src/core/or/congestion_control_vegas.c
new file mode 100644
index 0000000000..3206821f4c
--- /dev/null
+++ b/src/core/or/congestion_control_vegas.c
@@ -0,0 +1,200 @@
+/* Copyright (c) 2019-2021, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+/**
+ * \file congestion_control_vegas.c
+ * \brief Code that implements the TOR_VEGAS congestion control algorithm
+ *        from Proposal #324.
+ */
+
+#define TOR_CONGESTION_CONTROL_VEGAS_PRIVATE
+
+#include "core/or/or.h"
+
+#include "core/or/crypt_path.h"
+#include "core/or/or_circuit_st.h"
+#include "core/or/sendme.h"
+#include "core/or/congestion_control_st.h"
+#include "core/or/congestion_control_common.h"
+#include "core/or/congestion_control_vegas.h"
+#include "core/or/circuitlist.h"
+#include "core/or/circuituse.h"
+#include "core/or/origin_circuit_st.h"
+#include "core/or/channel.h"
+#include "feature/nodelist/networkstatus.h"
+
+#define VEGAS_GAMMA(cc)   (6*(cc)->sendme_inc)
+#define VEGAS_ALPHA(cc)   (3*(cc)->sendme_inc)
+#define VEGAS_BETA(cc)    (6*(cc)->sendme_inc)
+
+#define VEGAS_BDP_MIX_PCT       0
+
+/**
+ * The original TCP Vegas used only a congestion window BDP estimator. We
+ * believe that the piecewise estimator is likely to perform better, but
+ * for purposes of experimentation, we might as well have a way to blend
+ * them. It also lets us set Vegas to its original estimator while other
+ * algorithms on the same network use piecewise (by setting the
+ * 'vegas_bdp_mix_pct' consensus parameter to 100, while leaving the
+ * 'cc_bdp_alg' parameter set to piecewise).
+ *
+ * Returns a percentage weighted average between the CWND estimator and
+ * the specified consensus BDP estimator.
+ */
+static inline uint64_t
+vegas_bdp_mix(const congestion_control_t *cc)
+{
+  return cc->vegas_params.bdp_mix_pct*cc->bdp[BDP_ALG_CWND_RTT]/100 +
+         (100-cc->vegas_params.bdp_mix_pct)*cc->bdp[cc->bdp_alg]/100;
+}
+
+/**
+ * Cache Vegas consensus parameters.
+ */
+void
+congestion_control_vegas_set_params(congestion_control_t *cc)
+{
+  tor_assert(cc->cc_alg == CC_ALG_VEGAS);
+
+  cc->vegas_params.gamma =
+   networkstatus_get_param(NULL, "cc_vegas_gamma",
+      VEGAS_GAMMA(cc),
+      0,
+      1000);
+
+  cc->vegas_params.alpha =
+   networkstatus_get_param(NULL, "cc_vegas_alpha",
+      VEGAS_ALPHA(cc),
+      0,
+      1000);
+
+  cc->vegas_params.beta =
+   networkstatus_get_param(NULL, "cc_vegas_beta",
+      VEGAS_BETA(cc),
+      0,
+      1000);
+
+  cc->vegas_params.bdp_mix_pct =
+   networkstatus_get_param(NULL, "cc_vegas_bdp_mix",
+      VEGAS_BDP_MIX_PCT,
+      0,
+      100);
+}
+
+/**
+ * Process a SENDME and update the congestion window according to the
+ * rules specified in TOR_VEGAS of Proposal #324.
+ *
+ * Essentially, this algorithm attempts to measure queue lengths on
+ * the circuit by subtracting the bandwidth-delay-product estimate
+ * from the current congestion window.
+ *
+ * If the congestion window is larger than the bandwidth-delay-product,
+ * then data is assumed to be queuing. We reduce the congestion window
+ * in that case.
+ *
+ * If the congestion window is smaller than the bandwidth-delay-product,
+ * then there is spare bandwidth capacity on the circuit. We increase the
+ * congestion window in that case.
+ *
+ * The congestion window is updated only once every congestion window worth of
+ * packets, even if the signal persists. It is also updated whenever the
+ * upstream orcon blocks, or unblocks. This minimizes local client queues.
+ */
+int
+congestion_control_vegas_process_sendme(congestion_control_t *cc,
+                                        const circuit_t *circ,
+                                        const crypt_path_t *layer_hint)
+{
+  uint64_t queue_use;
+
+  tor_assert(cc && cc->cc_alg == CC_ALG_VEGAS);
+  tor_assert(circ);
+
+  /* Update ack counter until next congestion signal event is allowed */
+  if (cc->next_cc_event)
+    cc->next_cc_event--;
+
+  /* Compute BDP and RTT. If we did not update, don't run the alg */
+  if (!congestion_control_update_circuit_estimates(cc, circ, layer_hint)) {
+    cc->inflight = cc->inflight - cc->sendme_inc;
+    return 0;
+  }
+
+  /* We only update anything once per window */
+  if (cc->next_cc_event == 0) {
+    /* The queue use is the amount in which our cwnd is above BDP;
+     * if it is below, then 0 queue use. */
+    if (vegas_bdp_mix(cc) > cc->cwnd)
+      queue_use = 0;
+    else
+      queue_use = cc->cwnd - vegas_bdp_mix(cc);
+
+    if (cc->in_slow_start) {
+      if (queue_use < cc->vegas_params.gamma && !cc->blocked_chan) {
+        /* Grow to BDP immediately, then exponential growth until
+         * congestion signal */
+        cc->cwnd = MAX(cc->cwnd + CWND_INC_SS(cc),
+                       vegas_bdp_mix(cc));
+      } else {
+        /* Congestion signal: Fall back to Vegas equilibrium (BDP) */
+        cc->cwnd = vegas_bdp_mix(cc);
+        cc->in_slow_start = 0;
+        log_info(LD_CIRC, "CC: TOR_VEGAS exiting slow start");
+      }
+    } 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);
+      }
+    }
+
+    /* cwnd can never fall below 1 increment */
+    cc->cwnd = MAX(cc->cwnd, cc->cwnd_min);
+
+    /* Schedule next update */
+    cc->next_cc_event = CWND_UPDATE_RATE(cc);
+
+    if (CIRCUIT_IS_ORIGIN(circ)) {
+      log_info(LD_CIRC,
+                 "CC: TOR_VEGAS Circuit %d "
+                 "CWND: %"PRIu64", "
+                 "INFL: %"PRIu64", "
+                 "VBDP: %"PRIu64", "
+                 "QUSE: %"PRIu64", "
+                 "NCCE: %"PRIu64", "
+                 "SS: %d",
+               CONST_TO_ORIGIN_CIRCUIT(circ)->global_identifier,
+               cc->cwnd,
+               cc->inflight,
+               vegas_bdp_mix(cc),
+               queue_use,
+               cc->next_cc_event,
+               cc->in_slow_start
+               );
+    } else {
+      log_info(LD_CIRC,
+                 "CC: TOR_VEGAS Circuit %"PRIu64":%d "
+                 "CWND: %"PRIu64", "
+                 "INFL: %"PRIu64", "
+                 "VBDP: %"PRIu64", "
+                 "QUSE: %"PRIu64", "
+                 "NCCE: %"PRIu64", "
+                 "SS: %d",
+                 circ->n_chan->global_identifier, circ->n_circ_id,
+               cc->cwnd,
+               cc->inflight,
+               vegas_bdp_mix(cc),
+               queue_use,
+               cc->next_cc_event,
+               cc->in_slow_start
+               );
+    }
+  }
+
+  /* Update inflight with ack */
+  cc->inflight = cc->inflight - cc->sendme_inc;
+
+  return 0;
+}
diff --git a/src/core/or/congestion_control_vegas.h b/src/core/or/congestion_control_vegas.h
new file mode 100644
index 0000000000..111345081c
--- /dev/null
+++ b/src/core/or/congestion_control_vegas.h
@@ -0,0 +1,33 @@
+/* Copyright (c) 2019-2021, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+/**
+ * \file congestion_control_vegas.h
+ * \brief Private-ish APIs for the TOR_VEGAS congestion control algorithm
+ **/
+
+#ifndef TOR_CONGESTION_CONTROL_VEGAS_H
+#define TOR_CONGESTION_CONTROL_VEGAS_H
+
+#include "core/or/crypt_path_st.h"
+#include "core/or/circuit_st.h"
+
+/* Processing SENDME cell. */
+int congestion_control_vegas_process_sendme(struct congestion_control_t *cc,
+                                            const circuit_t *circ,
+                                            const crypt_path_t *layer_hint);
+void congestion_control_vegas_set_params(struct congestion_control_t *cc);
+
+/* Private section starts. */
+#ifdef TOR_CONGESTION_CONTROL_VEGAS_PRIVATE
+
+/*
+ * Unit tests declaractions.
+ */
+#ifdef TOR_UNIT_TESTS
+
+#endif /* defined(TOR_UNIT_TESTS) */
+
+#endif /* defined(TOR_CONGESTION_CONTROL_VEGAS_PRIVATE) */
+
+#endif /* !defined(TOR_CONGESTION_CONTROL_VEGAS_H) */