JianMin Liu 4442801a43 ANDROID: sched: Introducing PELT multiplier ...

The new sysctl sched_pelt_multiplier allows a user to set a clock
multiplier x2 or x4 (x1 being the default). This clock multiplier
artificially speed-up PELT ramp up/down similarly to a faster half-life.
Indeed, if we write PELT as a first order filter:

  y(t) = G * (1 - exp(t/tau))

Then we can see that multiplying the time by a constant X, is the same
as
dividing the time constant tau by X.

  y(t) = G * (1 - exp((t*X)/tau))
  y(t) = G * (1 - exp(t/(tau/X)))

Tau being half-life*ln(2), multiplying the PELT time is the same as
dividing the half-life:

  - x1: 32ms half-life
  - x2: 16ms half-life
  - x4: 8ms  half-life

Internally, a new clock is created: rq->clock_task_mult. It sits in the
clock hierarchy between rq->clock_task and rq->clock_pelt.

Bug: 177593580
Bug: 237219700
Change-Id: I67e6ca7994bebea22bf75732ee11d2b10e0d6b7e
Suggested-by: Morten Rasmussen <morten.rasmussen@arm.com>
Signed-off-by: Vincent Donnefort <vincent.donnefort@arm.com>
Signed-off-by: JianMin Liu <jian-min.liu@mediatek.com>

2022-07-27 21:20:26 +00:00

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