Messages in this thread | | | Date | Wed, 6 Sep 2023 14:56:57 +0200 | Subject | Re: [RFC PATCH 2/7] sched/pelt: Add a new function to approximate runtime to reach given util | From | Dietmar Eggemann <> |
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On 28/08/2023 01:31, Qais Yousef wrote: > It is basically the ramp-up time from 0 to a given value. Will be used > later to implement new tunable to control response time for schedutil. > > Signed-off-by: Qais Yousef (Google) <qyousef@layalina.io> > --- > kernel/sched/pelt.c | 21 +++++++++++++++++++++ > kernel/sched/sched.h | 1 + > 2 files changed, 22 insertions(+) > > diff --git a/kernel/sched/pelt.c b/kernel/sched/pelt.c > index 50322005a0ae..f673b9ab92dc 100644 > --- a/kernel/sched/pelt.c > +++ b/kernel/sched/pelt.c > @@ -487,3 +487,24 @@ unsigned long approximate_util_avg(unsigned long util, u64 delta) > > return sa.util_avg; > } > + > +/* > + * Approximate the required amount of runtime in ms required to reach @util. > + */ > +u64 approximate_runtime(unsigned long util) > +{ > + struct sched_avg sa = {}; > + u64 delta = 1024; // period = 1024 = ~1ms > + u64 runtime = 0; > + > + if (unlikely(!util)) > + return runtime; > + > + while (sa.util_avg < util) { > + accumulate_sum(delta, &sa, 0, 0, 1); > + ___update_load_avg(&sa, 0); > + runtime++; > + } > + > + return runtime; > +}
S_n = S_inv * (1 - 0.5^(t/hl))
t = hl * ln(1 - Sn/S_inv)/ln(0.5)
(1) for a little CPU (capacity_orig = 446)
t = 32ms * ln(1 - 446/1024)/ln(0.5)
t = 26ms
(2) for a big CPU (capacity = 1023 (*instead of 1024 since ln(0) not defined
t = 32ms * ln(1 - 1023/1024)/ln(0.5)
t = 320ms
[...]
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