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    SubjectRe: [patch 00/17] CFS Bandwidth Control v7.1

    * Paul Turner <pjt@google.com> wrote:

    > Finally introducing jump labels when there are no constrained
    > groups claws back a good portion of the remaining time.
    >
    > Add jump labels:
    > cycles instructions
    > branches
    > ----------------------------------------------------------------------------------------------------
    > base 893,486,206 840,904,951 160,076,980
    > +unconstrained 900,477,543 (+0.78) 890,310,950 (+5.88)
    > 161,037,844 (+0.60)
    > +10000000000/1000: 921,436,697 (+3.13) 919,362,792 (+9.33)
    > 168,491,279 (+5.26)
    > +10000000000/10000: 907,214,638 (+1.54) 894,406,875 (+6.36)
    > 165,743,207 (+3.54)
    > +10000000000/100000: 918,094,542 (+2.75) 910,211,234 (+8.24)
    > 167,841,828 (+4.85)
    > +10000000000/1000000: 910,698,725 (+1.93) 885,385,460 (+5.29)
    > 166,406,742 (+3.95)

    That looks pretty promising!

    The +5% instruction count still looks a tad high to me: if there are
    about 1000 instructions in this particular contex-switch critical
    path then 5% means +50 instructions - a 'disabled' feature sure
    should not use that many instructions, right?

    Also, i have a testing suggestion, i'd suggest to run:

    taskset 1 perf stat ...

    to only measure while pinned on a single CPU. This will remove a lot
    of cross-CPU noise from the context switching overhead.

    This is a valid way to progress because we are interested in the
    typical context-switch overhead on a single CPU - we know that
    there's no SMP cost when constraining is disabled.

    Doing that should bring your measurement noise below the 0.1% range i
    suspect. As you are shaving off cycle after cycle i think you'll need
    that kind of measurement precision ...

    Thanks,

    Ingo


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