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