resources/libraries/python/MLRsearch/MultipleLossRatioSearch.py

   1 # Copyright (c) 2018 Cisco and/or its affiliates.
   2 # Licensed under the Apache License, Version 2.0 (the "License");
   3 # you may not use this file except in compliance with the License.
   4 # You may obtain a copy of the License at:
   5 #
   6 #     http://www.apache.org/licenses/LICENSE-2.0
   7 #
   8 # Unless required by applicable law or agreed to in writing, software
   9 # distributed under the License is distributed on an "AS IS" BASIS,
  10 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  11 # See the License for the specific language governing permissions and
  12 # limitations under the License.
  13
  14 """Module defining MultipleLossRatioSearch class."""
  15
  16 import logging
  17 import math
  18 import time
  19
  20 from AbstractSearchAlgorithm import AbstractSearchAlgorithm
  21 from NdrPdrResult import NdrPdrResult
  22 from ReceiveRateInterval import ReceiveRateInterval
  23
  24
  25 class MultipleLossRatioSearch(AbstractSearchAlgorithm):
  26     """Optimized binary search algorithm for finding NDR and PDR bounds.
  27
  28     Traditional binary search algorithm needs initial interval
  29     (lower and upper bound), and returns final interval after bisecting
  30     (until some exit condition is met).
  31     The exit condition is usually related to the interval width,
  32     (upper bound value minus lower bound value).
  33
  34     The optimized algorithm contains several improvements
  35     aimed to reduce overall search time.
  36
  37     One improvement is searching for two intervals at once.
  38     The intervals are for NDR (No Drop Rate) and PDR (Partial Drop Rate).
  39
  40     Next improvement is that the initial interval does not need to be valid.
  41     Imagine initial interval (10, 11) where 11 is smaller
  42     than the searched value.
  43     The algorithm will try (11, 13) interval next, and if 13 is still smaller,
  44     (13, 17) and so on, doubling width until the upper bound is valid.
  45     The part when interval expands is called external search,
  46     the part when interval is bisected is called internal search.
  47
  48     Next improvement is that trial measurements at small trial duration
  49     can be used to find a reasonable interval for full trial duration search.
  50     This results in more trials performed, but smaller overall duration
  51     in general.
  52
  53     Next improvement is bisecting in logarithmic quantities,
  54     so that exit criteria can be independent of measurement units.
  55
  56     Next improvement is basing the initial interval on receive rates.
  57
  58     Final improvement is exiting early if the minimal value
  59     is not a valid lower bound.
  60
  61     The complete search consist of several phases,
  62     each phase performing several trial measurements.
  63     Initial phase creates initial interval based on receive rates
  64     at maximum rate and at maximum receive rate (MRR).
  65     Final phase and preceding intermediate phases are performing
  66     external and internal search steps,
  67     each resulting interval is the starting point for the next phase.
  68     The resulting interval of final phase is the result of the whole algorithm.
  69
  70     Each non-initial phase uses its own trial duration and width goal.
  71     Any non-initial phase stops searching (for NDR or PDR independently)
  72     when minimum is not a valid lower bound (at current duration),
  73     or all of the following is true:
  74     Both bounds are valid, bound bounds are measured at the current phase
  75     trial duration, interval width is less than the width goal
  76     for current phase.
  77
  78     TODO: Review and update this docstring according to rst docs.
  79     TODO: Support configurable number of Packet Loss Ratios.
  80     """
  81
  82     class ProgressState(object):
  83         """Structure containing data to be passed around in recursion."""
  84
  85         def __init__(
  86                 self, result, phases, duration, width_goal, packet_loss_ratio,
  87                 minimum_transmit_rate, maximum_transmit_rate):
  88             """Convert and store the argument values.
  89
  90             :param result: Current measured NDR and PDR intervals.
  91             :param phases: How many intermediate phases to perform
  92                 before the current one.
  93             :param duration: Trial duration to use in the current phase [s].
  94             :param width_goal: The goal relative width for the curreent phase.
  95             :param packet_loss_ratio: PDR fraction for the current search.
  96             :param minimum_transmit_rate: Minimum target transmit rate
  97                 for the current search [pps].
  98             :param maximum_transmit_rate: Maximum target transmit rate
  99                 for the current search [pps].
 100             :type result: NdrPdrResult.NdrPdrResult
 101             :type phases: int
 102             :type duration: float
 103             :type width_goal: float
 104             :type packet_loss_ratio: float
 105             :type minimum_transmit_rate: float
 106             :type maximum_transmit_rate: float
 107             """
 108             self.result = result
 109             self.phases = int(phases)
 110             self.duration = float(duration)
 111             self.width_goal = float(width_goal)
 112             self.packet_loss_ratio = float(packet_loss_ratio)
 113             self.minimum_transmit_rate = float(minimum_transmit_rate)
 114             self.maximum_transmit_rate = float(maximum_transmit_rate)
 115
 116     def __init__(self, measurer, final_relative_width=0.005,
 117                  final_trial_duration=30.0, initial_trial_duration=1.0,
 118                  number_of_intermediate_phases=2, timeout=600.0, doublings=1):
 119         """Store the measurer object and additional arguments.
 120
 121         :param measurer: Rate provider to use by this search object.
 122         :param final_relative_width: Final lower bound transmit rate
 123             cannot be more distant that this multiple of upper bound [1].
 124         :param final_trial_duration: Trial duration for the final phase [s].
 125         :param initial_trial_duration: Trial duration for the initial phase
 126             and also for the first intermediate phase [s].
 127         :param number_of_intermediate_phases: Number of intermediate phases
 128             to perform before the final phase [1].
 129         :param timeout: The search will fail itself when not finished
 130             before this overall time [s].
 131         :param doublings: How many doublings to do in external search step.
 132             Default 1 is suitable for fairly stable tests,
 133             less stable tests might get better overal duration with 2 or more.
 134         :type measurer: AbstractMeasurer.AbstractMeasurer
 135         :type final_relative_width: float
 136         :type final_trial_duration: float
 137         :type initial_trial_duration: int
 138         :type number_of_intermediate_phases: int
 139         :type timeout: float
 140         :type doublings: int
 141         """
 142         super(MultipleLossRatioSearch, self).__init__(measurer)
 143         self.final_trial_duration = float(final_trial_duration)
 144         self.final_relative_width = float(final_relative_width)
 145         self.number_of_intermediate_phases = int(number_of_intermediate_phases)
 146         self.initial_trial_duration = float(initial_trial_duration)
 147         self.timeout = float(timeout)
 148         self.doublings = int(doublings)
 149
 150
 151     @staticmethod
 152     def double_relative_width(relative_width):
 153         """Return relative width corresponding to double logarithmic width.
 154
 155         :param relative_width: The base relative width to double.
 156         :type relative_width: float
 157         :returns: The relative width of double logarithmic size.
 158         :rtype: float
 159         """
 160         return 1.999 * relative_width - relative_width * relative_width
 161         # The number should be 2.0, but we want to avoid rounding errors,
 162         # and ensure half of double is not larger than the original value.
 163
 164     @staticmethod
 165     def double_step_down(relative_width, current_bound):
 166         """Return rate of double logarithmic width below.
 167
 168         :param relative_width: The base relative width to double.
 169         :param current_bound: The current target transmit rate to move [pps].
 170         :type relative_width: float
 171         :type current_bound: float
 172         :returns: Transmit rate smaller by logarithmically double width [pps].
 173         :rtype: float
 174         """
 175         return current_bound * (
 176             1.0 - MultipleLossRatioSearch.double_relative_width(
 177                 relative_width))
 178
 179     @staticmethod
 180     def expand_down(relative_width, doublings, current_bound):
 181         """Return rate of expanded logarithmic width below.
 182
 183         :param relative_width: The base relative width to double.
 184         :param doublings: How many doublings to do for expansion.
 185         :param current_bound: The current target transmit rate to move [pps].
 186         :type relative_width: float
 187         :type doublings: int
 188         :type current_bound: float
 189         :returns: Transmit rate smaller by logarithmically double width [pps].
 190         :rtype: float
 191         """
 192         for _ in range(doublings):
 193             relative_width = MultipleLossRatioSearch.double_relative_width(
 194                 relative_width)
 195         return current_bound * (1.0 - relative_width)
 196
 197     @staticmethod
 198     def double_step_up(relative_width, current_bound):
 199         """Return rate of double logarithmic width above.
 200
 201         :param relative_width: The base relative width to double.
 202         :param current_bound: The current target transmit rate to move [pps].
 203         :type relative_width: float
 204         :type current_bound: float
 205         :returns: Transmit rate larger by logarithmically double width [pps].
 206         :rtype: float
 207         """
 208         return current_bound / (
 209             1.0 - MultipleLossRatioSearch.double_relative_width(
 210                 relative_width))
 211
 212     @staticmethod
 213     def expand_up(relative_width, doublings, current_bound):
 214         """Return rate of expanded logarithmic width above.
 215
 216         :param relative_width: The base relative width to double.
 217         :param doublings: How many doublings to do for expansion.
 218         :param current_bound: The current target transmit rate to move [pps].
 219         :type relative_width: float
 220         :type doublings: int
 221         :type current_bound: float
 222         :returns: Transmit rate smaller by logarithmically double width [pps].
 223         :rtype: float
 224         """
 225         for _ in range(doublings):
 226             relative_width = MultipleLossRatioSearch.double_relative_width(
 227                 relative_width)
 228         return current_bound / (1.0 - relative_width)
 229
 230     @staticmethod
 231     def half_relative_width(relative_width):
 232         """Return relative width corresponding to half logarithmic width.
 233
 234         :param relative_width: The base relative width to halve.
 235         :type relative_width: float
 236         :returns: The relative width of half logarithmic size.
 237         :rtype: float
 238         """
 239         return 1.0 - math.sqrt(1.0 - relative_width)
 240
 241     @staticmethod
 242     def half_step_up(relative_width, current_bound):
 243         """Return rate of half logarithmic width above.
 244
 245         :param relative_width: The base relative width to halve.
 246         :param current_bound: The current target transmit rate to move [pps].
 247         :type relative_width: float
 248         :type current_bound: float
 249         :returns: Transmit rate larger by logarithmically half width [pps].
 250         :rtype: float
 251         """
 252         return current_bound / (
 253             1.0 - MultipleLossRatioSearch.half_relative_width(relative_width))
 254
 255     def narrow_down_ndr_and_pdr(
 256             self, minimum_transmit_rate, maximum_transmit_rate,
 257             packet_loss_ratio):
 258         """Perform initial phase, create state object, proceed with next phases.
 259
 260         :param minimum_transmit_rate: Minimal target transmit rate [pps].
 261         :param maximum_transmit_rate: Maximal target transmit rate [pps].
 262         :param packet_loss_ratio: Fraction of packets lost, for PDR [1].
 263         :type minimum_transmit_rate: float
 264         :type maximum_transmit_rate: float
 265         :type packet_loss_ratio: float
 266         :returns: Structure containing narrowed down intervals
 267             and their measurements.
 268         :rtype: NdrPdrResult.NdrPdrResult
 269         :raises RuntimeError: If total duration is larger than timeout.
 270         """
 271         minimum_transmit_rate = float(minimum_transmit_rate)
 272         maximum_transmit_rate = float(maximum_transmit_rate)
 273         packet_loss_ratio = float(packet_loss_ratio)
 274         line_measurement = self.measurer.measure(
 275             self.initial_trial_duration, maximum_transmit_rate)
 276         initial_width_goal = self.final_relative_width
 277         for _ in range(self.number_of_intermediate_phases):
 278             initial_width_goal = self.double_relative_width(initial_width_goal)
 279         max_lo = maximum_transmit_rate * (1.0 - initial_width_goal)
 280         mrr = max(
 281             minimum_transmit_rate,
 282             min(max_lo, line_measurement.receive_rate))
 283         mrr_measurement = self.measurer.measure(
 284             self.initial_trial_duration, mrr)
 285         # Attempt to get narrower width.
 286         if mrr_measurement.loss_fraction > 0.0:
 287             max2_lo = mrr * (1.0 - initial_width_goal)
 288             mrr2 = min(max2_lo, mrr_measurement.receive_rate)
 289         else:
 290             mrr2 = mrr / (1.0 - initial_width_goal)
 291         if mrr2 > minimum_transmit_rate and mrr2 < maximum_transmit_rate:
 292             line_measurement = mrr_measurement
 293             mrr_measurement = self.measurer.measure(
 294                 self.initial_trial_duration, mrr2)
 295             if mrr2 > mrr:
 296                 buf = line_measurement
 297                 line_measurement = mrr_measurement
 298                 mrr_measurement = buf
 299         starting_interval = ReceiveRateInterval(
 300             mrr_measurement, line_measurement)
 301         starting_result = NdrPdrResult(starting_interval, starting_interval)
 302         state = self.ProgressState(
 303             starting_result, self.number_of_intermediate_phases,
 304             self.final_trial_duration, self.final_relative_width,
 305             packet_loss_ratio, minimum_transmit_rate, maximum_transmit_rate)
 306         state = self.ndrpdr(state)
 307         return state.result
 308
 309     def _measure_and_update_state(self, state, transmit_rate):
 310         """Perform trial measurement, update bounds, return new state.
 311
 312         :param state: State before this measurement.
 313         :param transmit_rate: Target transmit rate for this measurement [pps].
 314         :type state: ProgressState
 315         :type transmit_rate: float
 316         :returns: State after the measurement.
 317         :rtype: ProgressState
 318         """
 319         # TODO: Implement https://stackoverflow.com/a/24683360
 320         # to avoid the string manipulation if log verbosity is too low.
 321         logging.info("result before update: %s", state.result)
 322         logging.debug(
 323             "relative widths in goals: %s", state.result.width_in_goals(
 324                 self.final_relative_width))
 325         measurement = self.measurer.measure(state.duration, transmit_rate)
 326         ndr_interval = self._new_interval(
 327             state.result.ndr_interval, measurement, 0.0)
 328         pdr_interval = self._new_interval(
 329             state.result.pdr_interval, measurement, state.packet_loss_ratio)
 330         state.result = NdrPdrResult(ndr_interval, pdr_interval)
 331         return state
 332
 333     @staticmethod
 334     def _new_interval(old_interval, measurement, packet_loss_ratio):
 335         """Return new interval with bounds updated according to the measurement.
 336
 337         :param old_interval: The current interval before the measurement.
 338         :param measurement: The new meaqsurement to take into account.
 339         :param packet_loss_ratio: Fraction for PDR (or zero for NDR).
 340         :type old_interval: ReceiveRateInterval.ReceiveRateInterval
 341         :type measurement: ReceiveRateMeasurement.ReceiveRateMeasurement
 342         :type packet_loss_ratio: float
 343         :returns: The updated interval.
 344         :rtype: ReceiveRateInterval.ReceiveRateInterval
 345         """
 346         old_lo, old_hi = old_interval.measured_low, old_interval.measured_high
 347         # Priority zero: direct replace if the target Tr is the same.
 348         if measurement.target_tr in (old_lo.target_tr, old_hi.target_tr):
 349             if measurement.target_tr == old_lo.target_tr:
 350                 return ReceiveRateInterval(measurement, old_hi)
 351             else:
 352                 return ReceiveRateInterval(old_lo, measurement)
 353         # Priority one: invalid lower bound allows only one type of update.
 354         if old_lo.loss_fraction > packet_loss_ratio:
 355             # We can only expand down, old bound becomes valid upper one.
 356             if measurement.target_tr < old_lo.target_tr:
 357                 return ReceiveRateInterval(measurement, old_lo)
 358             else:
 359                 return old_interval
 360         # Lower bound is now valid.
 361         # Next priorities depend on target Tr.
 362         if measurement.target_tr < old_lo.target_tr:
 363             # Lower external measurement, relevant only
 364             # if the new measurement has high loss rate.
 365             if measurement.loss_fraction > packet_loss_ratio:
 366                 # Returning the broader interval as old_lo
 367                 # would be invalid upper bound.
 368                 return ReceiveRateInterval(measurement, old_hi)
 369         elif measurement.target_tr > old_hi.target_tr:
 370             # Upper external measurement, only relevant for invalid upper bound.
 371             if old_hi.loss_fraction <= packet_loss_ratio:
 372                 # Old upper bound becomes valid new lower bound.
 373                 return ReceiveRateInterval(old_hi, measurement)
 374         else:
 375             # Internal measurement, replaced boundary
 376             # depends on measured loss fraction.
 377             if measurement.loss_fraction > packet_loss_ratio:
 378                 # We have found a narrow valid interval,
 379                 # regardless of whether old upper bound was valid.
 380                 return ReceiveRateInterval(old_lo, measurement)
 381             else:
 382                 # In ideal world, we would not want to shrink interval
 383                 # if upper bound is not valid.
 384                 # In the real world, we want to shrink it for
 385                 # "invalid upper bound at maximal rate" case.
 386                 return ReceiveRateInterval(measurement, old_hi)
 387         # Fallback, the interval is unchanged by the measurement.
 388         return old_interval
 389
 390     def ndrpdr(self, state):
 391         """Pefrom trials for this phase. Return the new state when done.
 392
 393         :param state: State before this phase.
 394         :type state: ProgressState
 395         :returns: The updated state.
 396         :rtype: ProgressState
 397         :raises RuntimeError: If total duration is larger than timeout.
 398         """
 399         start_time = time.time()
 400         if state.phases > 0:
 401             # We need to finish preceding intermediate phases first.
 402             saved_phases = state.phases
 403             state.phases -= 1
 404             # Preceding phases have shorter duration.
 405             saved_duration = state.duration
 406             duration_multiplier = state.duration / self.initial_trial_duration
 407             phase_exponent = float(state.phases) / saved_phases
 408             state.duration = self.initial_trial_duration * math.pow(
 409                 duration_multiplier, phase_exponent)
 410             # Shorter durations do not need that narrow widths.
 411             saved_width = state.width_goal
 412             state.width_goal = self.double_relative_width(state.width_goal)
 413             # Recurse.
 414             state = self.ndrpdr(state)
 415             # Restore the state for current phase.
 416             state.duration = saved_duration
 417             state.width_goal = saved_width
 418             state.phases = saved_phases  # Not needed, but just in case.
 419         logging.info(
 420             "starting iterations with duration %s and relative width goal %s",
 421             state.duration, state.width_goal)
 422         while 1:
 423             if time.time() > start_time + self.timeout:
 424                 raise RuntimeError("Optimized search takes too long.")
 425             # Order of priorities: invalid bounds (nl, pl, nh, ph),
 426             # then narrowing relative Tr widths.
 427             # Durations are not priorities yet,
 428             # they will settle on their own hopefully.
 429             ndr_lo = state.result.ndr_interval.measured_low
 430             ndr_hi = state.result.ndr_interval.measured_high
 431             pdr_lo = state.result.pdr_interval.measured_low
 432             pdr_hi = state.result.pdr_interval.measured_high
 433             ndr_rel_width = max(
 434                 state.width_goal, state.result.ndr_interval.rel_tr_width)
 435             pdr_rel_width = max(
 436                 state.width_goal, state.result.pdr_interval.rel_tr_width)
 437             # If we are hitting maximal or minimal rate, we cannot shift,
 438             # but we can re-measure.
 439             if ndr_lo.loss_fraction > 0.0:
 440                 if ndr_lo.target_tr > state.minimum_transmit_rate:
 441                     new_tr = max(
 442                         state.minimum_transmit_rate,
 443                         self.expand_down(
 444                             ndr_rel_width, self.doublings, ndr_lo.target_tr))
 445                     logging.info("ndr lo external %s", new_tr)
 446                     state = self._measure_and_update_state(state, new_tr)
 447                     continue
 448                 elif ndr_lo.duration < state.duration:
 449                     logging.info("ndr lo minimal re-measure")
 450                     state = self._measure_and_update_state(
 451                         state, state.minimum_transmit_rate)
 452                     continue
 453             if pdr_lo.loss_fraction > state.packet_loss_ratio:
 454                 if pdr_lo.target_tr > state.minimum_transmit_rate:
 455                     new_tr = max(
 456                         state.minimum_transmit_rate,
 457                         self.expand_down(
 458                             pdr_rel_width, self.doublings, pdr_lo.target_tr))
 459                     logging.info("pdr lo external %s", new_tr)
 460                     state = self._measure_and_update_state(state, new_tr)
 461                     continue
 462                 elif pdr_lo.duration < state.duration:
 463                     logging.info("pdr lo minimal re-measure")
 464                     state = self._measure_and_update_state(
 465                         state, state.minimum_transmit_rate)
 466                     continue
 467             if ndr_hi.loss_fraction <= 0.0:
 468                 if ndr_hi.target_tr < state.maximum_transmit_rate:
 469                     new_tr = min(
 470                         state.maximum_transmit_rate,
 471                         self.expand_up(
 472                             ndr_rel_width, self.doublings, ndr_hi.target_tr))
 473                     logging.info("ndr hi external %s", new_tr)
 474                     state = self._measure_and_update_state(state, new_tr)
 475                     continue
 476                 elif ndr_hi.duration < state.duration:
 477                     logging.info("ndr hi maximal re-measure")
 478                     state = self._measure_and_update_state(
 479                         state, state.maximum_transmit_rate)
 480                     continue
 481             if pdr_hi.loss_fraction <= state.packet_loss_ratio:
 482                 if pdr_hi.target_tr < state.maximum_transmit_rate:
 483                     new_tr = min(
 484                         state.maximum_transmit_rate,
 485                         self.expand_up(
 486                             pdr_rel_width, self.doublings, pdr_hi.target_tr))
 487                     logging.info("pdr hi external %s", new_tr)
 488                     state = self._measure_and_update_state(state, new_tr)
 489                     continue
 490                 elif pdr_hi.duration < state.duration:
 491                     logging.info("ndr hi maximal re-measure")
 492                     state = self._measure_and_update_state(
 493                         state, state.maximum_transmit_rate)
 494                     continue
 495             # If we are hitting maximum_transmit_rate,
 496             # it is still worth narrowing width,
 497             # hoping large enough loss fraction will happen.
 498             # But if we are hitting the minimal rate (at current duration),
 499             # no additional measurement will help with that,
 500             # so we can stop narrowing in this phase.
 501             if (ndr_lo.target_tr <= state.minimum_transmit_rate
 502                     and ndr_lo.loss_fraction > 0.0):
 503                 ndr_rel_width = 0.0
 504             if (pdr_lo.target_tr <= state.minimum_transmit_rate
 505                     and pdr_lo.loss_fraction > state.packet_loss_ratio):
 506                 pdr_rel_width = 0.0
 507             if ndr_rel_width > state.width_goal:
 508                 # We have to narrow NDR width first, as NDR internal search
 509                 # can invalidate PDR (but not vice versa).
 510                 new_tr = self.half_step_up(ndr_rel_width, ndr_lo.target_tr)
 511                 logging.info("Bisecting for NDR at %s", new_tr)
 512                 state = self._measure_and_update_state(state, new_tr)
 513                 continue
 514             if pdr_rel_width > state.width_goal:
 515                 # PDR iternal search.
 516                 new_tr = self.half_step_up(pdr_rel_width, pdr_lo.target_tr)
 517                 logging.info("Bisecting for PDR at %s", new_tr)
 518                 state = self._measure_and_update_state(state, new_tr)
 519                 continue
 520             # We do not need to improve width, but there still might be
 521             # some measurements with smaller duration.
 522             # We need to re-measure with full duration, possibly
 523             # creating invalid bounds to resolve (thus broadening width).
 524             if ndr_lo.duration < state.duration:
 525                 logging.info("re-measuring NDR lower bound")
 526                 self._measure_and_update_state(state, ndr_lo.target_tr)
 527                 continue
 528             if pdr_lo.duration < state.duration:
 529                 logging.info("re-measuring PDR lower bound")
 530                 self._measure_and_update_state(state, pdr_lo.target_tr)
 531                 continue
 532             # Except when lower bounds have high loss fraction, in that case
 533             # we do not need to re-measure _upper_ bounds.
 534             if ndr_hi.duration < state.duration and ndr_rel_width > 0.0:
 535                 logging.info("re-measuring NDR upper bound")
 536                 self._measure_and_update_state(state, ndr_hi.target_tr)
 537                 continue
 538             if pdr_hi.duration < state.duration and pdr_rel_width > 0.0:
 539                 logging.info("re-measuring PDR upper bound")
 540                 self._measure_and_update_state(state, pdr_hi.target_tr)
 541                 continue
 542             # Widths are narrow (or lower bound minimal), bound measurements
 543             # are long enough, we can return.
 544             logging.info("phase done")
 545             break
 546         return state