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Diffstat (limited to 'src/or/circuitmux_ewma.c')
| -rw-r--r-- | src/or/circuitmux_ewma.c | 683 |
1 files changed, 683 insertions, 0 deletions
diff --git a/src/or/circuitmux_ewma.c b/src/or/circuitmux_ewma.c new file mode 100644 index 0000000000..c280bf4ab0 --- /dev/null +++ b/src/or/circuitmux_ewma.c @@ -0,0 +1,683 @@ +/* * Copyright (c) 2012, The Tor Project, Inc. */ +/* See LICENSE for licensing information */ + +/** + * \file circuitmux_ewma.c + * \brief EWMA circuit selection as a circuitmux_t policy + **/ + +#define _TOR_CIRCUITMUX_EWMA_C + +#include <math.h> + +#include "or.h" +#include "circuitmux.h" +#include "circuitmux_ewma.h" +#include "networkstatus.h" + +/*** EWMA parameter #defines ***/ + +/** How long does a tick last (seconds)? */ +#define EWMA_TICK_LEN 10 + +/** The default per-tick scale factor, if it hasn't been overridden by a + * consensus or a configuration setting. zero means "disabled". */ +#define EWMA_DEFAULT_HALFLIFE 0.0 + +/*** Some useful constant #defines ***/ + +/*DOCDOC*/ +#define EPSILON 0.00001 +/*DOCDOC*/ +#define LOG_ONEHALF -0.69314718055994529 + +/*** EWMA structures ***/ + +typedef struct cell_ewma_s cell_ewma_t; +typedef struct ewma_policy_data_s ewma_policy_data_t; +typedef struct ewma_policy_circ_data_s ewma_policy_circ_data_t; + +/** + * The cell_ewma_t structure keeps track of how many cells a circuit has + * transferred recently. It keeps an EWMA (exponentially weighted moving + * average) of the number of cells flushed from the circuit queue onto a + * connection in channel_flush_from_first_active_circuit(). + */ + +struct cell_ewma_s { + /** The last 'tick' at which we recalibrated cell_count. + * + * A cell sent at exactly the start of this tick has weight 1.0. Cells sent + * since the start of this tick have weight greater than 1.0; ones sent + * earlier have less weight. */ + unsigned int last_adjusted_tick; + /** The EWMA of the cell count. */ + double cell_count; + /** True iff this is the cell count for a circuit's previous + * channel. */ + unsigned int is_for_p_chan : 1; + /** The position of the circuit within the OR connection's priority + * queue. */ + int heap_index; +}; + +struct ewma_policy_data_s { + circuitmux_policy_data_t _base; + + /** + * Priority queue of cell_ewma_t for circuits with queued cells waiting + * for room to free up on the channel that owns this circuitmux. Kept + * in heap order according to EWMA. This was formerly in channel_t, and + * in or_connection_t before that. + */ + smartlist_t *active_circuit_pqueue; + + /** + * The tick on which the cell_ewma_ts in active_circuit_pqueue last had + * their ewma values rescaled. This was formerly in channel_t, and in + * or_connection_t before that. + */ + unsigned int active_circuit_pqueue_last_recalibrated; +}; + +struct ewma_policy_circ_data_s { + circuitmux_policy_circ_data_t _base; + + /** + * The EWMA count for the number of cells flushed from this circuit + * onto this circuitmux. Used to determine which circuit to flush + * from next. This was formerly in circuit_t and or_circuit_t. + */ + cell_ewma_t cell_ewma; + + /** + * Pointer back to the circuit_t this is for; since we're separating + * out circuit selection policy like this, we can't attach cell_ewma_t + * to the circuit_t any more, so we can't use SUBTYPE_P directly to a + * circuit_t like before; instead get it here. + */ + circuit_t *circ; +}; + +#define EWMA_POL_DATA_MAGIC 0x2fd8b16aU +#define EWMA_POL_CIRC_DATA_MAGIC 0x761e7747U + +/*** Downcasts for the above types ***/ + +static ewma_policy_data_t * +TO_EWMA_POL_DATA(circuitmux_policy_data_t *); + +static ewma_policy_circ_data_t * +TO_EWMA_POL_CIRC_DATA(circuitmux_policy_circ_data_t *); + +/** + * Downcast a circuitmux_policy_data_t to an ewma_policy_data_t and assert + * if the cast is impossible. + */ + +static INLINE ewma_policy_data_t * +TO_EWMA_POL_DATA(circuitmux_policy_data_t *pol) +{ + if (!pol) return NULL; + else { + tor_assert(pol->magic == EWMA_POL_DATA_MAGIC); + return DOWNCAST(ewma_policy_data_t, pol); + } +} + +/** + * Downcast a circuitmux_policy_circ_data_t to an ewma_policy_circ_data_t + * and assert if the cast is impossible. + */ + +static INLINE ewma_policy_circ_data_t * +TO_EWMA_POL_CIRC_DATA(circuitmux_policy_circ_data_t *pol) +{ + if (!pol) return NULL; + else { + tor_assert(pol->magic == EWMA_POL_CIRC_DATA_MAGIC); + return DOWNCAST(ewma_policy_circ_data_t, pol); + } +} + +/*** Static declarations for circuitmux_ewma.c ***/ + +static void add_cell_ewma(ewma_policy_data_t *pol, cell_ewma_t *ewma); +static int compare_cell_ewma_counts(const void *p1, const void *p2); +static unsigned cell_ewma_tick_from_timeval(const struct timeval *now, + double *remainder_out); +static circuit_t * cell_ewma_to_circuit(cell_ewma_t *ewma); +static INLINE double get_scale_factor(unsigned from_tick, unsigned to_tick); +static cell_ewma_t * pop_first_cell_ewma(ewma_policy_data_t *pol); +static void remove_cell_ewma(ewma_policy_data_t *pol, cell_ewma_t *ewma); +static void scale_single_cell_ewma(cell_ewma_t *ewma, unsigned cur_tick); +static void scale_active_circuits(ewma_policy_data_t *pol, + unsigned cur_tick); + +/*** Circuitmux policy methods ***/ + +static circuitmux_policy_data_t * ewma_alloc_cmux_data(circuitmux_t *cmux); +static void ewma_free_cmux_data(circuitmux_t *cmux, + circuitmux_policy_data_t *pol_data); +static circuitmux_policy_circ_data_t * +ewma_alloc_circ_data(circuitmux_t *cmux, circuitmux_policy_data_t *pol_data, + circuit_t *circ, cell_direction_t direction, + unsigned int cell_count); +static void +ewma_free_circ_data(circuitmux_t *cmux, + circuitmux_policy_data_t *pol_data, + circuit_t *circ, + circuitmux_policy_circ_data_t *pol_circ_data); +static void +ewma_notify_circ_active(circuitmux_t *cmux, + circuitmux_policy_data_t *pol_data, + circuit_t *circ, + circuitmux_policy_circ_data_t *pol_circ_data); +static void +ewma_notify_circ_inactive(circuitmux_t *cmux, + circuitmux_policy_data_t *pol_data, + circuit_t *circ, + circuitmux_policy_circ_data_t *pol_circ_data); +static void +ewma_notify_xmit_cells(circuitmux_t *cmux, + circuitmux_policy_data_t *pol_data, + circuit_t *circ, + circuitmux_policy_circ_data_t *pol_circ_data, + unsigned int n_cells); +static circuit_t * +ewma_pick_active_circuit(circuitmux_t *cmux, + circuitmux_policy_data_t *pol_data); + +/*** EWMA global variables ***/ + +/** The per-tick scale factor to be used when computing cell-count EWMA + * values. (A cell sent N ticks before the start of the current tick + * has value ewma_scale_factor ** N.) + */ +static double ewma_scale_factor = 0.1; +/* DOCDOC ewma_enabled */ +static int ewma_enabled = 0; + +/*** EWMA circuitmux_policy_t method table ***/ + +circuitmux_policy_t ewma_policy = { .alloc_cmux_data = ewma_alloc_cmux_data, + .free_cmux_data = ewma_free_cmux_data, + .alloc_circ_data = ewma_alloc_circ_data, + .free_circ_data = ewma_free_circ_data, + .notify_circ_active = ewma_notify_circ_active, + .notify_circ_inactive = ewma_notify_circ_inactive, + .notify_set_n_cells = NULL, /* EWMA doesn't need this */ + .notify_xmit_cells = ewma_notify_xmit_cells, + .pick_active_circuit = ewma_pick_active_circuit +}; + +/*** EWMA method implementations using the below EWMA helper functions ***/ + +/** + * Allocate an ewma_policy_data_t and upcast it to a circuitmux_policy_data_t; + * this is called when setting the policy on a circuitmux_t to ewma_policy. + */ + +static circuitmux_policy_data_t * +ewma_alloc_cmux_data(circuitmux_t *cmux) +{ + ewma_policy_data_t *pol = NULL; + + tor_assert(cmux); + + pol = tor_malloc_zero(sizeof(*pol)); + pol->_base.magic = EWMA_POL_DATA_MAGIC; + pol->active_circuit_pqueue = smartlist_new(); + pol->active_circuit_pqueue_last_recalibrated = cell_ewma_get_tick(); + + return TO_CMUX_POL_DATA(pol); +} + +/** + * Free an ewma_policy_data_t allocated with ewma_alloc_cmux_data() + */ + +static void +ewma_free_cmux_data(circuitmux_t *cmux, + circuitmux_policy_data_t *pol_data) +{ + ewma_policy_data_t *pol = NULL; + + tor_assert(cmux); + if (!pol_data) return; + + pol = TO_EWMA_POL_DATA(pol_data); + + smartlist_free(pol->active_circuit_pqueue); + tor_free(pol); +} + +/** + * Allocate an ewma_policy_circ_data_t and upcast it to a + * circuitmux_policy_data_t; this is called when attaching a circuit to a + * circuitmux_t with ewma_policy. + */ + +static circuitmux_policy_circ_data_t * +ewma_alloc_circ_data(circuitmux_t *cmux, + circuitmux_policy_data_t *pol_data, + circuit_t *circ, + cell_direction_t direction, + unsigned int cell_count) +{ + ewma_policy_circ_data_t *cdata = NULL; + + tor_assert(cmux); + tor_assert(pol_data); + tor_assert(circ); + tor_assert(direction == CELL_DIRECTION_OUT || + direction == CELL_DIRECTION_IN); + /* Shut the compiler up */ + tor_assert(cell_count == cell_count); + + cdata = tor_malloc_zero(sizeof(*cdata)); + cdata->_base.magic = EWMA_POL_CIRC_DATA_MAGIC; + cdata->circ = circ; + + /* + * Initialize the cell_ewma_t structure (formerly in + * init_circuit_base()) + */ + cdata->cell_ewma.last_adjusted_tick = cell_ewma_get_tick(); + cdata->cell_ewma.cell_count = 0.0; + cdata->cell_ewma.heap_index = -1; + if (direction == CELL_DIRECTION_IN) { + cdata->cell_ewma.is_for_p_chan = 1; + } else { + cdata->cell_ewma.is_for_p_chan = 0; + } + + return TO_CMUX_POL_CIRC_DATA(cdata); +} + +/** + * Free an ewma_policy_circ_data_t allocated with ewma_alloc_circ_data() + */ + +static void +ewma_free_circ_data(circuitmux_t *cmux, + circuitmux_policy_data_t *pol_data, + circuit_t *circ, + circuitmux_policy_circ_data_t *pol_circ_data) + +{ + ewma_policy_circ_data_t *cdata = NULL; + + tor_assert(cmux); + tor_assert(circ); + tor_assert(pol_data); + + if (!pol_circ_data) return; + + cdata = TO_EWMA_POL_CIRC_DATA(pol_circ_data); + + tor_free(cdata); +} + +/** + * Handle circuit activation; this inserts the circuit's cell_ewma into + * the active_circuits_pqueue. + */ + +static void +ewma_notify_circ_active(circuitmux_t *cmux, + circuitmux_policy_data_t *pol_data, + circuit_t *circ, + circuitmux_policy_circ_data_t *pol_circ_data) +{ + ewma_policy_data_t *pol = NULL; + ewma_policy_circ_data_t *cdata = NULL; + + tor_assert(cmux); + tor_assert(pol_data); + tor_assert(circ); + tor_assert(pol_circ_data); + + pol = TO_EWMA_POL_DATA(pol_data); + cdata = TO_EWMA_POL_CIRC_DATA(pol_circ_data); + + add_cell_ewma(pol, &(cdata->cell_ewma)); +} + +/** + * Handle circuit deactivation; this removes the circuit's cell_ewma from + * the active_circuits_pqueue. + */ + +static void +ewma_notify_circ_inactive(circuitmux_t *cmux, + circuitmux_policy_data_t *pol_data, + circuit_t *circ, + circuitmux_policy_circ_data_t *pol_circ_data) +{ + ewma_policy_data_t *pol = NULL; + ewma_policy_circ_data_t *cdata = NULL; + + tor_assert(cmux); + tor_assert(pol_data); + tor_assert(circ); + tor_assert(pol_circ_data); + + pol = TO_EWMA_POL_DATA(pol_data); + cdata = TO_EWMA_POL_CIRC_DATA(pol_circ_data); + + remove_cell_ewma(pol, &(cdata->cell_ewma)); +} + +/** + * Update cell_ewma for this circuit after we've sent some cells, and + * remove/reinsert it in the queue. This used to be done (brokenly, + * see bug 6816) in channel_flush_from_first_active_circuit(). + */ + +static void +ewma_notify_xmit_cells(circuitmux_t *cmux, + circuitmux_policy_data_t *pol_data, + circuit_t *circ, + circuitmux_policy_circ_data_t *pol_circ_data, + unsigned int n_cells) +{ + ewma_policy_data_t *pol = NULL; + ewma_policy_circ_data_t *cdata = NULL; + unsigned int tick; + double fractional_tick, ewma_increment; + /* The current (hi-res) time */ + struct timeval now_hires; + cell_ewma_t *cell_ewma, *tmp; + + tor_assert(cmux); + tor_assert(pol_data); + tor_assert(circ); + tor_assert(pol_circ_data); + tor_assert(n_cells > 0); + + pol = TO_EWMA_POL_DATA(pol_data); + cdata = TO_EWMA_POL_CIRC_DATA(pol_circ_data); + + /* Rescale the EWMAs if needed */ + tor_gettimeofday_cached(&now_hires); + tick = cell_ewma_tick_from_timeval(&now_hires, &fractional_tick); + + if (tick != pol->active_circuit_pqueue_last_recalibrated) { + scale_active_circuits(pol, tick); + } + + /* How much do we adjust the cell count in cell_ewma by? */ + ewma_increment = + ((double)(n_cells)) * pow(ewma_scale_factor, -fractional_tick); + + /* Do the adjustment */ + cell_ewma = &(cdata->cell_ewma); + cell_ewma->cell_count += ewma_increment; + + /* + * Since we just sent on this circuit, it should be at the head of + * the queue. Pop the head, assert that it matches, then re-add. + */ + tmp = pop_first_cell_ewma(pol); + tor_assert(tmp == cell_ewma); + add_cell_ewma(pol, cell_ewma); +} + +/** + * Pick the preferred circuit to send from; this will be the one with + * the lowest EWMA value in the priority queue. This used to be done + * in channel_flush_from_first_active_circuit(). + */ + +static circuit_t * +ewma_pick_active_circuit(circuitmux_t *cmux, + circuitmux_policy_data_t *pol_data) +{ + ewma_policy_data_t *pol = NULL; + circuit_t *circ = NULL; + cell_ewma_t *cell_ewma = NULL; + + tor_assert(cmux); + tor_assert(pol_data); + + pol = TO_EWMA_POL_DATA(pol_data); + + if (smartlist_len(pol->active_circuit_pqueue) > 0) { + /* Get the head of the queue */ + cell_ewma = smartlist_get(pol->active_circuit_pqueue, 0); + circ = cell_ewma_to_circuit(cell_ewma); + } + + return circ; +} + +/** Helper for sorting cell_ewma_t values in their priority queue. */ +static int +compare_cell_ewma_counts(const void *p1, const void *p2) +{ + const cell_ewma_t *e1 = p1, *e2 = p2; + + if (e1->cell_count < e2->cell_count) + return -1; + else if (e1->cell_count > e2->cell_count) + return 1; + else + return 0; +} + +/** Given a cell_ewma_t, return a pointer to the circuit containing it. */ +static circuit_t * +cell_ewma_to_circuit(cell_ewma_t *ewma) +{ + ewma_policy_circ_data_t *cdata = NULL; + + tor_assert(ewma); + cdata = SUBTYPE_P(ewma, ewma_policy_circ_data_t, cell_ewma); + tor_assert(cdata); + + return cdata->circ; +} + +/* ==== Functions for scaling cell_ewma_t ==== + + When choosing which cells to relay first, we favor circuits that have been + quiet recently. This gives better latency on connections that aren't + pushing lots of data, and makes the network feel more interactive. + + Conceptually, we take an exponentially weighted mean average of the number + of cells a circuit has sent, and allow active circuits (those with cells to + relay) to send cells in reverse order of their exponentially-weighted mean + average (EWMA) cell count. [That is, a cell sent N seconds ago 'counts' + F^N times as much as a cell sent now, for 0<F<1.0, and we favor the + circuit that has sent the fewest cells] + + If 'double' had infinite precision, we could do this simply by counting a + cell sent at startup as having weight 1.0, and a cell sent N seconds later + as having weight F^-N. This way, we would never need to re-scale + any already-sent cells. + + To prevent double from overflowing, we could count a cell sent now as + having weight 1.0 and a cell sent N seconds ago as having weight F^N. + This, however, would mean we'd need to re-scale *ALL* old circuits every + time we wanted to send a cell. + + So as a compromise, we divide time into 'ticks' (currently, 10-second + increments) and say that a cell sent at the start of a current tick is + worth 1.0, a cell sent N seconds before the start of the current tick is + worth F^N, and a cell sent N seconds after the start of the current tick is + worth F^-N. This way we don't overflow, and we don't need to constantly + rescale. + */ + +/** Given a timeval <b>now</b>, compute the cell_ewma tick in which it occurs + * and the fraction of the tick that has elapsed between the start of the tick + * and <b>now</b>. Return the former and store the latter in + * *<b>remainder_out</b>. + * + * These tick values are not meant to be shared between Tor instances, or used + * for other purposes. */ + +static unsigned +cell_ewma_tick_from_timeval(const struct timeval *now, + double *remainder_out) +{ + unsigned res = (unsigned) (now->tv_sec / EWMA_TICK_LEN); + /* rem */ + double rem = (now->tv_sec % EWMA_TICK_LEN) + + ((double)(now->tv_usec)) / 1.0e6; + *remainder_out = rem / EWMA_TICK_LEN; + return res; +} + +/** Tell the caller whether ewma_enabled is set */ +int +cell_ewma_enabled(void) +{ + return ewma_enabled; +} + +/** Compute and return the current cell_ewma tick. */ +unsigned int +cell_ewma_get_tick(void) +{ + return ((unsigned)approx_time() / EWMA_TICK_LEN); +} + +/** Adjust the global cell scale factor based on <b>options</b> */ +void +cell_ewma_set_scale_factor(const or_options_t *options, + const networkstatus_t *consensus) +{ + int32_t halflife_ms; + double halflife; + const char *source; + if (options && options->CircuitPriorityHalflife >= -EPSILON) { + halflife = options->CircuitPriorityHalflife; + source = "CircuitPriorityHalflife in configuration"; + } else if (consensus && (halflife_ms = networkstatus_get_param( + consensus, "CircuitPriorityHalflifeMsec", + -1, -1, INT32_MAX)) >= 0) { + halflife = ((double)halflife_ms)/1000.0; + source = "CircuitPriorityHalflifeMsec in consensus"; + } else { + halflife = EWMA_DEFAULT_HALFLIFE; + source = "Default value"; + } + + if (halflife <= EPSILON) { + /* The cell EWMA algorithm is disabled. */ + ewma_scale_factor = 0.1; + ewma_enabled = 0; + log_info(LD_OR, + "Disabled cell_ewma algorithm because of value in %s", + source); + } else { + /* convert halflife into halflife-per-tick. */ + halflife /= EWMA_TICK_LEN; + /* compute per-tick scale factor. */ + ewma_scale_factor = exp( LOG_ONEHALF / halflife ); + ewma_enabled = 1; + log_info(LD_OR, + "Enabled cell_ewma algorithm because of value in %s; " + "scale factor is %f per %d seconds", + source, ewma_scale_factor, EWMA_TICK_LEN); + } +} + +/** Return the multiplier necessary to convert the value of a cell sent in + * 'from_tick' to one sent in 'to_tick'. */ +static INLINE double +get_scale_factor(unsigned from_tick, unsigned to_tick) +{ + /* This math can wrap around, but that's okay: unsigned overflow is + well-defined */ + int diff = (int)(to_tick - from_tick); + return pow(ewma_scale_factor, diff); +} + +/** Adjust the cell count of <b>ewma</b> so that it is scaled with respect to + * <b>cur_tick</b> */ +static void +scale_single_cell_ewma(cell_ewma_t *ewma, unsigned cur_tick) +{ + double factor = get_scale_factor(ewma->last_adjusted_tick, cur_tick); + ewma->cell_count *= factor; + ewma->last_adjusted_tick = cur_tick; +} + +/** Adjust the cell count of every active circuit on <b>chan</b> so + * that they are scaled with respect to <b>cur_tick</b> */ +static void +scale_active_circuits(ewma_policy_data_t *pol, unsigned cur_tick) +{ + double factor; + + tor_assert(pol); + tor_assert(pol->active_circuit_pqueue); + + factor = + get_scale_factor( + pol->active_circuit_pqueue_last_recalibrated, + cur_tick); + /** Ordinarily it isn't okay to change the value of an element in a heap, + * but it's okay here, since we are preserving the order. */ + SMARTLIST_FOREACH_BEGIN( + pol->active_circuit_pqueue, + cell_ewma_t *, e) { + tor_assert(e->last_adjusted_tick == + pol->active_circuit_pqueue_last_recalibrated); + e->cell_count *= factor; + e->last_adjusted_tick = cur_tick; + } SMARTLIST_FOREACH_END(e); + pol->active_circuit_pqueue_last_recalibrated = cur_tick; +} + +/** Rescale <b>ewma</b> to the same scale as <b>pol</b>, and add it to + * <b>pol</b>'s priority queue of active circuits */ +static void +add_cell_ewma(ewma_policy_data_t *pol, cell_ewma_t *ewma) +{ + tor_assert(pol); + tor_assert(pol->active_circuit_pqueue); + tor_assert(ewma); + tor_assert(ewma->heap_index == -1); + + scale_single_cell_ewma( + ewma, + pol->active_circuit_pqueue_last_recalibrated); + + smartlist_pqueue_add(pol->active_circuit_pqueue, + compare_cell_ewma_counts, + STRUCT_OFFSET(cell_ewma_t, heap_index), + ewma); +} + +/** Remove <b>ewma</b> from <b>pol</b>'s priority queue of active circuits */ +static void +remove_cell_ewma(ewma_policy_data_t *pol, cell_ewma_t *ewma) +{ + tor_assert(pol); + tor_assert(pol->active_circuit_pqueue); + tor_assert(ewma); + tor_assert(ewma->heap_index != -1); + + smartlist_pqueue_remove(pol->active_circuit_pqueue, + compare_cell_ewma_counts, + STRUCT_OFFSET(cell_ewma_t, heap_index), + ewma); +} + +/** Remove and return the first cell_ewma_t from pol's priority queue of + * active circuits. Requires that the priority queue is nonempty. */ +static cell_ewma_t * +pop_first_cell_ewma(ewma_policy_data_t *pol) +{ + tor_assert(pol); + tor_assert(pol->active_circuit_pqueue); + + return smartlist_pqueue_pop(pol->active_circuit_pqueue, + compare_cell_ewma_counts, + STRUCT_OFFSET(cell_ewma_t, heap_index)); +} + |