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Update all the histogram functions to use the new design.
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changes/bug29298
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6
changes/bug29298
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@ -0,0 +1,6 @@
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o Minor features (circuit padding):
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- Allow the padding machine designer to pick the edges of their histogram
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instead of trying to compute them automatically using an exponential
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formula. Resolves some undefined behavior in the case of small histograms
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and allows greater flexibility on machine design. Closes ticket 29298;
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bugfix on 0.4.0.1-alpha.
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@ -222,25 +222,15 @@ circpad_machine_current_state(const circpad_machine_state_t *mi)
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}
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/**
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* Calculate the lower bound of a histogram bin. The upper bound
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* is obtained by calling this function with bin+1, and subtracting 1.
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*
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* The 0th bin has a special value -- it only represents start_usec.
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* This is so we can specify a probability on 0-delay values.
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*
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* After bin 0, bins are exponentially spaced, so that each subsequent
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* bin is twice as large as the previous. This is done so that higher
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* time resolution is given to lower time values.
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*
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* The infinity bin is a the last bin in the array (histogram_len-1).
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* It has a usec value of CIRCPAD_DELAY_INFINITE (UINT32_MAX).
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* Get the lower bound of a histogram bin. The upper bound is obtained by
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* calling this function with bin+1, and subtracting 1.
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*/
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STATIC circpad_delay_t
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circpad_histogram_bin_to_usec(const circpad_machine_state_t *mi,
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circpad_hist_index_t bin)
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{
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const circpad_state_t *state = circpad_machine_current_state(mi);
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circpad_delay_t start_usec;
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circpad_delay_t rtt_add_usec = 0;
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/* Our state should have been checked to be non-null by the caller
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* (circpad_machine_remove_token()) */
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@ -248,27 +238,29 @@ circpad_histogram_bin_to_usec(const circpad_machine_state_t *mi,
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return CIRCPAD_DELAY_INFINITE;
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}
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if (state->use_rtt_estimate)
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start_usec = mi->rtt_estimate_usec+state->start_usec;
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else
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start_usec = state->start_usec;
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if (bin >= CIRCPAD_INFINITY_BIN(state))
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/* The infinity bin has an upper bound of infinity, so make sure we return
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* that if they ask for it. */
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if (bin > CIRCPAD_INFINITY_BIN(mi)) {
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return CIRCPAD_DELAY_INFINITE;
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}
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if (bin == 0)
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return start_usec;
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/* If we are using an RTT estimate, consider it as well. */
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if (state->use_rtt_estimate) {
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rtt_add_usec = mi->rtt_estimate_usec;
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}
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if (bin == 1)
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return start_usec+1;
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return state->histogram_edges[bin] + rtt_add_usec;
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}
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/* The bin widths double every index, so that we can have more resolution
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* for lower time values in the histogram. */
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const circpad_time_t bin_width_exponent =
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1 << (CIRCPAD_INFINITY_BIN(state) - bin);
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return (circpad_delay_t)MIN(start_usec +
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state->range_usec/bin_width_exponent,
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CIRCPAD_DELAY_INFINITE);
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/**
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* Like circpad_histogram_bin_to_usec() but return the upper bound of bin.
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* (The upper bound is included in the bin.)
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*/
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STATIC circpad_delay_t
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histogram_get_bin_upper_bound(const circpad_machine_state_t *mi,
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circpad_hist_index_t bin)
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{
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return circpad_histogram_bin_to_usec(mi, bin+1) - 1;
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}
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/** Return the midpoint of the histogram bin <b>bin_index</b>. */
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@ -287,19 +279,17 @@ circpad_get_histogram_bin_midpoint(const circpad_machine_state_t *mi,
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* Return the bin that contains the usec argument.
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* "Contains" is defined as us in [lower, upper).
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*
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* This function will never return the infinity bin (histogram_len-1),
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* in order to simplify the rest of the code.
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*
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* This means that technically the last bin (histogram_len-2)
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* has range [start_usec+range_usec, CIRCPAD_DELAY_INFINITE].
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* This function will never return the infinity bin (histogram_len-1), in order
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* to simplify the rest of the code, so if a usec is provided that falls above
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* the highest non-infinity bin, that bin index will be returned.
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*/
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STATIC circpad_hist_index_t
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circpad_histogram_usec_to_bin(const circpad_machine_state_t *mi,
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circpad_delay_t usec)
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{
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const circpad_state_t *state = circpad_machine_current_state(mi);
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circpad_delay_t start_usec;
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int32_t bin; /* Larger than return type to properly clamp overflow */
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circpad_delay_t rtt_add_usec = 0;
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int32_t bin;
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/* Our state should have been checked to be non-null by the caller
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* (circpad_machine_remove_token()) */
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@ -307,34 +297,25 @@ circpad_histogram_usec_to_bin(const circpad_machine_state_t *mi,
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return 0;
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}
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if (state->use_rtt_estimate)
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start_usec = mi->rtt_estimate_usec+state->start_usec;
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else
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start_usec = state->start_usec;
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/* If we are using an RTT estimate, consider it as well. */
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if (state->use_rtt_estimate) {
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rtt_add_usec = mi->rtt_estimate_usec;
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}
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/* The first bin (#0) has zero width and starts (and ends) at start_usec. */
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if (usec <= start_usec)
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return 0;
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/* Walk through the bins and check the upper bound of each bin, if 'usec' is
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* less-or-equal to that, return that bin. If rtt_estimate is enabled then
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* add that to the upper bound of each bin.
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*
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* We don't want to return the infinity bin here, so don't go there. */
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for (bin = 0 ; bin < CIRCPAD_INFINITY_BIN(state) ; bin++) {
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if (usec <= histogram_get_bin_upper_bound(mi, bin) + rtt_add_usec) {
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return bin;
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}
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}
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if (usec == start_usec+1)
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return 1;
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const circpad_time_t histogram_range_usec = state->range_usec;
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/* We need to find the bin corresponding to our position in the range.
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* Since bins are exponentially spaced in powers of two, we need to
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* take the log2 of our position in histogram_range_usec. However,
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* since tor_log2() returns the floor(log2(u64)), we have to adjust
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* it to behave like ceil(log2(u64)). This is verified in our tests
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* to properly invert the operation done in
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* circpad_histogram_bin_to_usec(). */
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bin = CIRCPAD_INFINITY_BIN(state) -
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tor_log2(2*histogram_range_usec/(usec-start_usec+1));
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/* Clamp the return value to account for timevals before the start
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* of bin 0, or after the last bin. Don't return the infinity bin
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* index. */
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bin = MIN(MAX(bin, 1), CIRCPAD_INFINITY_BIN(state)-1);
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return bin;
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/* We don't want to return the infinity bin here, so if we still didn't find
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* the right bin, return the highest non-infinity bin */
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return CIRCPAD_INFINITY_BIN(state)-1;
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}
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/**
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@ -506,10 +487,6 @@ circpad_machine_sample_delay(circpad_machine_state_t *mi)
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* function below samples from [bin_start, bin_end) */
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bin_end = circpad_histogram_bin_to_usec(mi, curr_bin+1);
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/* Truncate the high bin in case it's the infinity bin:
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* Don't actually schedule an "infinite"-1 delay */
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bin_end = MIN(bin_end, start_usec+state->range_usec);
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// Sample uniformly between histogram[i] to histogram[i+1]-1,
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// but no need to sample if they are the same timeval (aka bin 0 or bin 1).
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if (bin_end <= bin_start+1)
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@ -621,7 +598,7 @@ circpad_machine_first_higher_index(const circpad_machine_state_t *mi,
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/* Don't remove from the infinity bin */
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for (; bin < CIRCPAD_INFINITY_BIN(mi); bin++) {
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if (mi->histogram[bin] &&
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circpad_histogram_bin_to_usec(mi, bin+1) > target_bin_usec) {
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histogram_get_bin_upper_bound(mi, bin) >= target_bin_usec) {
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return bin;
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}
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}
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@ -710,6 +710,10 @@ circpad_send_command_to_hop,(struct origin_circuit_t *circ, uint8_t hopnum,
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uint8_t relay_command, const uint8_t *payload,
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ssize_t payload_len));
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STATIC circpad_delay_t
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histogram_get_bin_upper_bound(const circpad_machine_state_t *mi,
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circpad_hist_index_t bin);
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#ifdef TOR_UNIT_TESTS
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extern smartlist_t *origin_padding_machines;
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extern smartlist_t *relay_padding_machines;
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