calc_cbs_params.py

#!/usr/bin/env python
#
# Copyright (c) 2017, Intel Corporation
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import argparse
import math

def print_cbs_params_for_class_a(args):
    idleslope = args.idleslope_a
    sendslope = idleslope - args.link_speed

    # According to 802.1Q-2014 spec, Annex L, hiCredit and
    # loCredit for SR class A are calculated following the
    # equations L-10 and L-12, respectively.
    hicredit = math.ceil(idleslope * args.frame_non_sr / args.link_speed)
    locredit = math.ceil(sendslope * args.frame_a / args.link_speed)

    print("tc qdisc add dev <IFNAME> parent <QDISC-ID> cbs idleslope %d sendslope %d hicredit %d locredit %d" % \
          (idleslope, sendslope, hicredit, locredit))

def print_cbs_params_for_class_b(args):
    idleslope = args.idleslope_b
    sendslope = idleslope - args.link_speed

    # Annex L doesn't present a straightforward equation to
    # calculate hiCredit for Class B so we have to derive it
    # based on generic equations presented in that Annex.
    #
    # L-3 is the primary equation to calculate hiCredit. Section
    # L.2 states that the 'maxInterferenceSize' for SR class B
    # is the maximum burst size for SR class A plus the
    # maxInterferenceSize from SR class A (which is equal to the
    # maximum frame from non-SR traffic).
    #
    # The maximum burst size for SR class A equation is shown in
    # L-16. Merging L-16 into L-3 we get the resulting equation
    # which calculates hiCredit B (refer to section L.3 in case
    # you're not familiar with the legend):
    #
    # hiCredit B = Rb * (     Mo         Ma   )
    #                     ---------- + ------
    #                      Ro - Ra       Ro
    #
    hicredit = math.ceil(idleslope * \
               ((args.frame_non_sr / (args.link_speed - args.idleslope_a)) + \
               (args.frame_a / args.link_speed)))

    # loCredit B is calculated following equation L-2.
    locredit = math.ceil(sendslope * args.frame_b / args.link_speed)

    print("tc qdisc add dev <IFNAME> parent <QDISC-ID> cbs idleslope %d sendslope %d hicredit %d locredit %d" % \
          (idleslope, sendslope, hicredit, locredit))

def main():
    parser = argparse.ArgumentParser()

    parser.add_argument('-S', dest='link_speed', default=1000000.0, type=float,
                        help='Link speed in kbps')
    parser.add_argument('-s', dest='frame_non_sr', default=1500.0, type=float,
                        help='Maximum frame size from non-SR traffic (MTU size'
                        'usually')
    parser.add_argument('-A', dest='idleslope_a', default=0, type=float,
                        help='Idleslope for SR class A in kbps')
    parser.add_argument('-a', dest='frame_a', default=0, type=float,
                        help='Maximum frame size for SR class A traffic')
    parser.add_argument('-B', dest='idleslope_b', default=0, type=float,
                        help='Idleslope for SR class B in kbps')
    parser.add_argument('-b', dest='frame_b', default=0, type=float,
                        help='Maximum frame size for SR class B traffic')

    args = parser.parse_args()

    if args.idleslope_a > 0:
        print_cbs_params_for_class_a(args)

    if args.idleslope_b > 0:
        print_cbs_params_for_class_b(args)

if __name__ == "__main__":
    main()