linux-kernel - Re: [PATCH 6/6] cpufreq: schedutil: New governor based on scheduler utilization data

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Date:	Thu, 3 Mar 2016 19:58:23 +0100
From:	"Rafael J. Wysocki" <rafael@...nel.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Vincent Guittot <vincent.guittot@...aro.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Linux PM list <linux-pm@...r.kernel.org>,
	Juri Lelli <juri.lelli@....com>,
	Steve Muckle <steve.muckle@...aro.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Michael Turquette <mturquette@...libre.com>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH 6/6] cpufreq: schedutil: New governor based on scheduler
 utilization data

On Thu, Mar 3, 2016 at 5:28 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Thu, Mar 03, 2016 at 04:38:17PM +0100, Peter Zijlstra wrote:
>> On Thu, Mar 03, 2016 at 03:01:15PM +0100, Vincent Guittot wrote:
>> > > In case a more formal derivation of this formula is needed, it is
>> > > based on the following 3 assumptions:
>> > >
>> > > (1) Performance is a linear function of frequency.
>> > > (2) Required performance is a linear function of the utilization ratio
>> > > x = util/max as provided by the scheduler (0 <= x <= 1).
>> >
>> > Just to mention that the utilization that you are using, varies with
>> > the frequency which add another variable in your equation
>>
>> Right, x86 hasn't implemented arch_scale_freq_capacity(), so the
>> utilization values we use are all over the map. If we lower freq, the
>> util will go up, which would result in us bumping the freq again, etc..
>
> Something like the completely untested below should maybe work.
>
> Rafael?

It looks reasonable (modulo the MPERF reading typo you've noticed),
but can we get back to that later?

I'll first try to address the Ingo's feedback (which I hope I
understood correctly) and some other comments people had and resend
the series.

> ---
>  arch/x86/include/asm/topology.h | 19 +++++++++++++++++++
>  arch/x86/kernel/smpboot.c       | 24 ++++++++++++++++++++++++
>  kernel/sched/core.c             |  1 +
>  kernel/sched/sched.h            |  7 +++++++
>  4 files changed, 51 insertions(+)
>
> diff --git a/arch/x86/include/asm/topology.h b/arch/x86/include/asm/topology.h
> index 7f991bd5031b..af7b7259db94 100644
> --- a/arch/x86/include/asm/topology.h
> +++ b/arch/x86/include/asm/topology.h
> @@ -146,4 +146,23 @@ struct pci_bus;
>  int x86_pci_root_bus_node(int bus);
>  void x86_pci_root_bus_resources(int bus, struct list_head *resources);
>
> +#ifdef CONFIG_SMP
> +
> +#define arch_scale_freq_tick arch_scale_freq_tick
> +#define arch_scale_freq_capacity arch_scale_freq_capacity
> +
> +DECLARE_PER_CPU(unsigned long, arch_cpu_freq);
> +
> +static inline arch_scale_freq_capacity(struct sched_domain *sd, int cpu)
> +{
> +       if (static_cpu_has(X86_FEATURE_APERFMPERF))
> +               return per_cpu(arch_cpu_freq, cpu);
> +       else
> +               return SCHED_CAPACITY_SCALE;
> +}
> +
> +extern void arch_scale_freq_tick(void);
> +
> +#endif
> +
>  #endif /* _ASM_X86_TOPOLOGY_H */
> diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
> index 3bf1e0b5f827..7d459577ee44 100644
> --- a/arch/x86/kernel/smpboot.c
> +++ b/arch/x86/kernel/smpboot.c
> @@ -1647,3 +1647,27 @@ void native_play_dead(void)
>  }
>
>  #endif
> +
> +static DEFINE_PER_CPU(u64, arch_prev_aperf);
> +static DEFINE_PER_CPU(u64, arch_prev_mperf);
> +DEFINE_PER_CPU(unsigned long, arch_cpu_freq);
> +
> +void arch_scale_freq_tick(void)
> +{
> +       u64 aperf, mperf;
> +       u64 acnt, mcnt;
> +
> +       if (!static_cpu_has(X86_FEATURE_APERFMPERF))
> +               return;
> +
> +       aperf = rdmsrl(MSR_IA32_APERF);
> +       mperf = rdmsrl(MSR_IA32_APERF);
> +
> +       acnt = aperf - this_cpu_read(arch_prev_aperf);
> +       mcnt = mperf - this_cpu_read(arch_prev_mperf);
> +
> +       this_cpu_write(arch_prev_aperf, aperf);
> +       this_cpu_write(arch_prev_mperf, mperf);
> +
> +       this_cpu_write(arch_cpu_freq, div64_u64(acnt * SCHED_CAPACITY_SCALE, mcnt));
> +}
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 96e323b26ea9..35dbf909afb2 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2901,6 +2901,7 @@ void scheduler_tick(void)
>         struct rq *rq = cpu_rq(cpu);
>         struct task_struct *curr = rq->curr;
>
> +       arch_scale_freq_tick();
>         sched_clock_tick();
>
>         raw_spin_lock(&rq->lock);
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index baa32075f98e..c3825c920e3f 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -1408,6 +1408,13 @@ unsigned long arch_scale_freq_capacity(struct sched_domain *sd, int cpu)
>  }
>  #endif
>
> +#ifndef arch_scale_freq_tick
> +static __always_inline
> +void arch_scale_freq_tick(void)
> +{
> +}
> +#endif
> +
>  #ifndef arch_scale_cpu_capacity
>  static __always_inline
>  unsigned long arch_scale_cpu_capacity(struct sched_domain *sd, int cpu)