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Diffstat (limited to 'src/core/or/congestion_control_vegas.c')
| -rw-r--r-- | src/core/or/congestion_control_vegas.c | 200 |
1 files changed, 200 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; +} |