Messages in this thread | | | Date | Wed, 7 Feb 2024 11:40:03 +0000 | Subject | Re: [PATCH v7 15/23] PM: EM: Optimize em_cpu_energy() and remove division | From | Hongyan Xia <> |
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On 17/01/2024 09:57, Lukasz Luba wrote: > The Energy Model (EM) can be modified at runtime which brings new > possibilities. The em_cpu_energy() is called by the Energy Aware Scheduler > (EAS) in its hot path. The energy calculation uses power value for > a given performance state (ps) and the CPU busy time as percentage for that > given frequency. > > It is possible to avoid the division by 'scale_cpu' at runtime, because > EM is updated whenever new max capacity CPU is set in the system. > > Use that feature and do the needed division during the calculation of the > coefficient 'ps->cost'. That enhanced 'ps->cost' value can be then just > multiplied simply by utilization: > > pd_nrg = ps->cost * \Sum cpu_util > > to get the needed energy for whole Performance Domain (PD). > > With this optimization and earlier removal of map_util_freq(), the > em_cpu_energy() should run faster on the Big CPU by 1.43x and on the Little > CPU by 1.69x (RockPi 4B board). > > Signed-off-by: Lukasz Luba <lukasz.luba@arm.com> > --- > include/linux/energy_model.h | 54 ++++++++++-------------------------- > kernel/power/energy_model.c | 7 ++--- > 2 files changed, 17 insertions(+), 44 deletions(-) > > diff --git a/include/linux/energy_model.h b/include/linux/energy_model.h > index 689d71f6b56f..aabfc26fcd31 100644 > --- a/include/linux/energy_model.h > +++ b/include/linux/energy_model.h > [...] > @@ -208,8 +206,9 @@ static int em_compute_costs(struct device *dev, struct em_perf_state *table, > return -EINVAL; > } > } else { > - power_res = table[i].power; > - cost = div64_u64(fmax * power_res, table[i].frequency); > + /* increase resolution of 'cost' precision */ > + power_res = table[i].power * 10;
NIT: Does this have to be 10, or something simple like << 3 (* 8) also does the job?
Although compiler these days often are clever enough to convert x * 10 into (x << 3) + (x << 1), and this is not on the hot path anyway, so just a NIT.
> + cost = power_res / table[i].performance; > } > > table[i].cost = cost;
Reviewed-by: Hongyan Xia <hongyan.xia2@arm.com>
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