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    SubjectRe: [PATCH 5/5] powercap/drivers/dtpm: Scale the power with the load
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    Hi Daniel,

    I've started reviewing the series, please find some comments below.

    On 3/1/21 9:21 PM, Daniel Lezcano wrote:
    > Currently the power consumption is based on the current OPP power
    > assuming the entire performance domain is fully loaded.
    >
    > That gives very gross power estimation and we can do much better by
    > using the load to scale the power consumption.
    >
    > Use the utilization to normalize and scale the power usage over the
    > max possible power.
    >
    > Tested on a rock960 with 2 big CPUS, the power consumption estimation
    > conforms with the expected one.
    >
    > Before this change:
    >
    > ~$ ~/dhrystone -t 1 -l 10000&
    > ~$ cat /sys/devices/virtual/powercap/dtpm/dtpm:0/dtpm:0:1/constraint_0_max_power_uw
    > 2260000
    >
    > After this change:
    >
    > ~$ ~/dhrystone -t 1 -l 10000&
    > ~$ cat /sys/devices/virtual/powercap/dtpm/dtpm:0/dtpm:0:1/constraint_0_max_power_uw
    > 1130000
    >
    > ~$ ~/dhrystone -t 2 -l 10000&
    > ~$ cat /sys/devices/virtual/powercap/dtpm/dtpm:0/dtpm:0:1/constraint_0_max_power_uw
    > 2260000
    >
    > Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
    > ---
    > drivers/powercap/dtpm_cpu.c | 21 +++++++++++++++++----
    > 1 file changed, 17 insertions(+), 4 deletions(-)
    >
    > diff --git a/drivers/powercap/dtpm_cpu.c b/drivers/powercap/dtpm_cpu.c
    > index e728ebd6d0ca..8379b96468ef 100644
    > --- a/drivers/powercap/dtpm_cpu.c
    > +++ b/drivers/powercap/dtpm_cpu.c
    > @@ -68,27 +68,40 @@ static u64 set_pd_power_limit(struct dtpm *dtpm, u64 power_limit)
    > return power_limit;
    > }
    >
    > +static u64 scale_pd_power_uw(struct cpumask *cpus, u64 power)

    renamed 'cpus' into 'pd_mask', see below

    > +{
    > + unsigned long max, util;
    > + int cpu, load = 0;

    IMHO 'int load' looks odd when used with 'util' and 'max'.
    I would put in the line above to have them all the same type and
    renamed to 'sum_util'.

    > +
    > + for_each_cpu(cpu, cpus) {

    I would avoid the temporary CPU mask in the get_pd_power_uw()
    with this modified loop:

    for_each_cpu_and(cpu, pd_mask, cpu_online_mask) {


    > + max = arch_scale_cpu_capacity(cpu);
    > + util = sched_cpu_util(cpu, max);
    > + load += ((util * 100) / max);

    Below you can find 3 optimizations. Since we are not in the hot
    path here, it's up to if you would like to use all/some of them
    or just ignore.

    1st optimization.
    If we use 'load += (util << 10) / max' in the loop, then
    we could avoid div by 100 and use a right shift:
    (power * load) >> 10

    2nd optimization.
    Since we use EM CPU mask, which span all CPUs with the same
    arch_scale_cpu_capacity(), you can avoid N divs inside the loop
    and do it once, below the loop.

    3rd optimization.
    If we just simply add all 'util' into 'sum_util' (no mul or div in
    the loop), then we might just have simple macro

    #define CALC_POWER_USAGE(power, sum_util, max) \
    (((power * (sum_util << 10)) / max) >> 10)


    > + }
    > +
    > + return (power * load) / 100;
    > +}
    > +
    > static u64 get_pd_power_uw(struct dtpm *dtpm)
    > {
    > struct dtpm_cpu *dtpm_cpu = to_dtpm_cpu(dtpm);
    > struct em_perf_domain *pd;
    > struct cpumask cpus;

    Since we don't need the 'nr_cpus' we also don't need the
    cpumask which occupy stack; Maybe use
    struct cpumask *pd_mask;

    then

    > unsigned long freq;
    > - int i, nr_cpus;
    > + int i;
    >
    > pd = em_cpu_get(dtpm_cpu->cpu);
    > freq = cpufreq_quick_get(dtpm_cpu->cpu);
    >
    > cpumask_and(&cpus, cpu_online_mask, to_cpumask(pd->cpus));

    remove ^^^^^ and set
    pd_mask = em_span_cpus(pd);

    > - nr_cpus = cpumask_weight(&cpus);
    >
    > for (i = 0; i < pd->nr_perf_states; i++) {
    >
    > if (pd->table[i].frequency < freq)
    > continue;
    >
    > - return pd->table[i].power *
    > - MICROWATT_PER_MILLIWATT * nr_cpus;
    > + return scale_pd_power_uw(&cpus, pd->table[i].power *
    > + MICROWATT_PER_MILLIWATT);

    Instead of '&cpus' I would put 'pd_mask' and that should do the job.

    > }
    >
    > return 0;
    >

    Apart from that, the design idea with util looks good.

    Regards,
    Lukasz

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