Messages in this thread | | | Date | Wed, 6 Sep 2023 22:44:14 +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 06/09/2023 14:56, Dietmar Eggemann wrote: > 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
Forgot half of what I wanted to ask:
And you want to be able to have a schedutil interface:
/sys/devices/system/cpu/cpufreq/policy*/schedutil/response_time_ms
in which by default we have 26ms for a CPU with the capacity_orig of 446.
I.e. you want to have a time-based interface there? Which the user can overwrite, say with 52ms and this then will lower the return value of get_next_freq() so the system will respond slower?
And the time based interface is more intuitive than staying in the capacity world of [0-1024]?
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