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SubjectRe: [Patch v5 6/6] sched/fair: Enable tuning of decay period
On Wed, Nov 6, 2019 at 12:20 AM Thara Gopinath
<thara.gopinath@linaro.org> wrote:
>
> Thermal pressure follows pelt signas which means the
> decay period for thermal pressure is the default pelt
> decay period. Depending on soc charecteristics and thermal
> activity, it might be beneficial to decay thermal pressure
> slower, but still in-tune with the pelt signals.
> One way to achieve this is to provide a command line parameter
> to set a decay shift parameter to an integer between 0 and 10.
>
> Signed-off-by: Thara Gopinath <thara.gopinath@linaro.org>
> ---
>
> v4->v5:
> - Changed _coeff to _shift as per review comments on the list.
>
> Documentation/admin-guide/kernel-parameters.txt | 5 +++++
> kernel/sched/fair.c | 25 +++++++++++++++++++++++--
> 2 files changed, 28 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index c82f87c..0b8f55e 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -4281,6 +4281,11 @@
> incurs a small amount of overhead in the scheduler
> but is useful for debugging and performance tuning.
>
> + sched_thermal_decay_shift=
> + [KNL, SMP] Set decay shift for thermal pressure signal.
> + Format: integer betweer 0 and 10
> + Default is 0.
> +
> skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
> xtime_lock contention on larger systems, and/or RCU lock
> contention on all systems with CONFIG_MAXSMP set.
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 5f6c371..61a020b 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -91,6 +91,18 @@ const_debug unsigned int sysctl_sched_migration_cost = 500000UL;
> * and maximum available capacity due to thermal events.
> */
> static DEFINE_PER_CPU(unsigned long, thermal_pressure);
> +/**
> + * By default the decay is the default pelt decay period.
> + * The decay shift can change the decay period in
> + * multiples of 32.
> + * Decay shift Decay period(ms)
> + * 0 32
> + * 1 64
> + * 2 128
> + * 3 256
> + * 4 512
> + */
> +static int sched_thermal_decay_shift;
>
> static void trigger_thermal_pressure_average(struct rq *rq);
>
> @@ -10435,6 +10447,15 @@ void update_thermal_pressure(int cpu, unsigned long capped_capacity)
> delta = arch_scale_cpu_capacity(cpu) - capped_capacity;
> per_cpu(thermal_pressure, cpu) = delta;
> }
> +
> +static int __init setup_sched_thermal_decay_shift(char *str)
> +{
> + if (kstrtoint(str, 0, &sched_thermal_decay_shift))
> + pr_warn("Unable to set scheduler thermal pressure decay shift parameter\n");

You're reading straight from the cmdline into a kernel variable w/o
any bounds checking. Perhaps use clamp or clamp_val to make sure it is
between 0 and 10?


> +
> + return 1;
> +}
> +__setup("sched_thermal_decay_shift=", setup_sched_thermal_decay_shift);
> #endif
>
> /**
> @@ -10444,8 +10465,8 @@ void update_thermal_pressure(int cpu, unsigned long capped_capacity)
> static void trigger_thermal_pressure_average(struct rq *rq)
> {
> #ifdef CONFIG_SMP
> - update_thermal_load_avg(rq_clock_task(rq), rq,
> - per_cpu(thermal_pressure, cpu_of(rq)));
> + update_thermal_load_avg(rq_clock_task(rq) >> sched_thermal_decay_shift,
> + rq, per_cpu(thermal_pressure, cpu_of(rq)));
> #endif
> }
>
> --
> 2.1.4
>

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