Re: [RFCv5, 01/46] arm: Frequency invariant scheduler load-tracking support

Leo Yan
2015-07-21T15:41:58Z

Hi Morten,

On Tue, Jul 07, 2015 at 07:23:44PM +0100, Morten Rasmussen wrote:
> From: Morten Rasmussen <Morten.Rasmussen@arm.com>
>
> Implements arch-specific function to provide the scheduler with a
> frequency scaling correction factor for more accurate load-tracking.
> The factor is:
>
> current_freq(cpu) << SCHED_CAPACITY_SHIFT / max_freq(cpu)
>
> This implementation only provides frequency invariance. No cpu
> invariance yet.
>
> Cc: Russell King <linux@arm.linux.org.uk>
>
> Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
>
> ---
> arch/arm/include/asm/topology.h | 7 +++++
> arch/arm/kernel/smp.c | 57 +++++++++++++++++++++++++++++++++++++++--
> arch/arm/kernel/topology.c | 17 ++++++++++++
> 3 files changed, 79 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm/include/asm/topology.h b/arch/arm/include/asm/topology.h
> index 370f7a7..c31096f 100644
> --- a/arch/arm/include/asm/topology.h
> +++ b/arch/arm/include/asm/topology.h
> @@ -24,6 +24,13 @@ void init_cpu_topology(void);
> void store_cpu_topology(unsigned int cpuid);
> const struct cpumask *cpu_coregroup_mask(int cpu);
>
> +#define arch_scale_freq_capacity arm_arch_scale_freq_capacity
> +struct sched_domain;
> +extern
> +unsigned long arm_arch_scale_freq_capacity(struct sched_domain *sd, int cpu);
> +
> +DECLARE_PER_CPU(atomic_long_t, cpu_freq_capacity);
> +
> #else
>
> static inline void init_cpu_topology(void) { }
> diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
> index cca5b87..a32539c 100644
> --- a/arch/arm/kernel/smp.c
> +++ b/arch/arm/kernel/smp.c
> @@ -677,12 +677,34 @@ static DEFINE_PER_CPU(unsigned long, l_p_j_ref);
> static DEFINE_PER_CPU(unsigned long, l_p_j_ref_freq);
> static unsigned long global_l_p_j_ref;
> static unsigned long global_l_p_j_ref_freq;
> +static DEFINE_PER_CPU(atomic_long_t, cpu_max_freq);
> +DEFINE_PER_CPU(atomic_long_t, cpu_freq_capacity);
> +
> +/*
> + * Scheduler load-tracking scale-invariance
> + *
> + * Provides the scheduler with a scale-invariance correction factor that
> + * compensates for frequency scaling through arch_scale_freq_capacity()
> + * (implemented in topology.c).
> + */
> +static inline
> +void scale_freq_capacity(int cpu, unsigned long curr, unsigned long max)
> +{
> + unsigned long capacity;
> +
> + if (!max)
> + return;
> +
> + capacity = (curr << SCHED_CAPACITY_SHIFT) / max;
> + atomic_long_set(&per_cpu(cpu_freq_capacity, cpu), capacity);
> +}
>
> static int cpufreq_callback(struct notifier_block *nb,
> unsigned long val, void *data)
> {
> struct cpufreq_freqs *freq = data;
> int cpu = freq->cpu;
> + unsigned long max = atomic_long_read(&per_cpu(cpu_max_freq, cpu));
>
> if (freq->flags & CPUFREQ_CONST_LOOPS)
> return NOTIFY_OK;
> @@ -707,6 +729,10 @@ static int cpufreq_callback(struct notifier_block *nb,
> per_cpu(l_p_j_ref_freq, cpu),
> freq->new);
> }
> +
> + if (val == CPUFREQ_PRECHANGE)
> + scale_freq_capacity(cpu, freq->new, max);
> +
> return NOTIFY_OK;
> }
>
> @@ -714,11 +740,38 @@ static struct notifier_block cpufreq_notifier = {
> .notifier_call = cpufreq_callback,
> };
>
> +static int cpufreq_policy_callback(struct notifier_block *nb,
> + unsigned long val, void *data)
> +{
> + struct cpufreq_policy *policy = data;
> + int i;
> +
> + if (val != CPUFREQ_NOTIFY)
> + return NOTIFY_OK;
> +
> + for_each_cpu(i, policy->cpus) {
> + scale_freq_capacity(i, policy->cur, policy->max);
> + atomic_long_set(&per_cpu(cpu_max_freq, i), policy->max);
> + }
> +
> + return NOTIFY_OK;
> +}
> +
> +static struct notifier_block cpufreq_policy_notifier = {
> + .notifier_call = cpufreq_policy_callback,
> +};
> +
> static int __init register_cpufreq_notifier(void)
> {
> - return cpufreq_register_notifier(&cpufreq_notifier,
> + int ret;
> +
> + ret = cpufreq_register_notifier(&cpufreq_notifier,
> CPUFREQ_TRANSITION_NOTIFIER);
> + if (ret)
> + return ret;
> +
> + return cpufreq_register_notifier(&cpufreq_policy_notifier,
> + CPUFREQ_POLICY_NOTIFIER);
> }
> core_initcall(register_cpufreq_notifier);

For "cpu_freq_capacity" structure, could move it into driver/cpufreq
so that it can be shared by all architectures? Otherwise, every
architecture's smp.c need register notifier for themselves.

Thanks,
Leo Yan

> -
> #endif
> diff --git a/arch/arm/kernel/topology.c b/arch/arm/kernel/topology.c
> index 08b7847..9c09e6e 100644
> --- a/arch/arm/kernel/topology.c
> +++ b/arch/arm/kernel/topology.c
> @@ -169,6 +169,23 @@ static void update_cpu_capacity(unsigned int cpu)
> cpu, arch_scale_cpu_capacity(NULL, cpu));
> }
>
> +/*
> + * Scheduler load-tracking scale-invariance
> + *
> + * Provides the scheduler with a scale-invariance correction factor that
> + * compensates for frequency scaling (arch_scale_freq_capacity()). The scaling
> + * factor is updated in smp.c
> + */
> +unsigned long arm_arch_scale_freq_capacity(struct sched_domain *sd, int cpu)
> +{
> + unsigned long curr = atomic_long_read(&per_cpu(cpu_freq_capacity, cpu));
> +
> + if (!curr)
> + return SCHED_CAPACITY_SCALE;
> +
> + return curr;
> +}
> +
> #else
> static inline void parse_dt_topology(void) {}
> static inline void update_cpu_capacity(unsigned int cpuid) {}