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Message-ID: <2258456.tKf67v4TDG@vostro.rjw.lan>
Date: Sat, 23 May 2015 01:43:07 +0200
From: "Rafael J. Wysocki" <rjw@...ysocki.net>
To: Michael Turquette <mturquette@...aro.org>
Cc: peterz@...radead.org, mingo@...nel.org,
linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
preeti@...ux.vnet.ibm.com, Morten.Rasmussen@....com,
riel@...hat.com, efault@....de, nicolas.pitre@...aro.org,
daniel.lezcano@...aro.org, dietmar.eggemann@....com,
vincent.guittot@...aro.org, amit.kucheria@...aro.org,
juri.lelli@....com, viresh.kumar@...aro.org,
ashwin.chaugule@...aro.org, alex.shi@...aro.org,
abelvesa@...il.com, Russell King <linux@....linux.org.uk>,
Morten Rasmussen <morten.rasmussen@....com>
Subject: Re: [PATCH RFC v2 1/4] arm: Frequency invariant scheduler load-tracking support
On Monday, May 11, 2015 07:13:12 PM Michael Turquette wrote:
> From: Morten Rasmussen <Morten.Rasmussen@....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
> micro-architecture invariance yet.
>
> Cc: Russell King <linux@....linux.org.uk>
> Signed-off-by: Morten Rasmussen <morten.rasmussen@....com>
> ---
> Changes in v2:
> none
>
> arch/arm/include/asm/topology.h | 7 ++++++
> arch/arm/kernel/smp.c | 53 +++++++++++++++++++++++++++++++++++++++--
> arch/arm/kernel/topology.c | 17 +++++++++++++
> 3 files changed, 75 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm/include/asm/topology.h b/arch/arm/include/asm/topology.h
> index 2fe85ff..4b985dc 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 86ef244..297ce1b 100644
> --- a/arch/arm/kernel/smp.c
> +++ b/arch/arm/kernel/smp.c
> @@ -672,12 +672,34 @@ 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;
> @@ -702,6 +724,9 @@ static int cpufreq_callback(struct notifier_block *nb,
> per_cpu(l_p_j_ref_freq, cpu),
> freq->new);
> }
> +
> + scale_freq_capacity(cpu, freq->new, max);
> +
> return NOTIFY_OK;
> }
>
> @@ -709,11 +734,35 @@ 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;
> +
> + 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);
> -
> #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) {}
I'm not sure if I'm reading this correctly, but what exactly is ARM-specific
in this new code?
Could it be made generic, in particular?
--
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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