Message-ID: <20210119191550.GB19274@arm.com>
Date:   Tue, 19 Jan 2021 19:17:25 +0000
From:   Ionela Voinescu <ionela.voinescu@....com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Rafael Wysocki <rjw@...ysocki.net>, linux-pm@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Peter Puhov <peter.puhov@...aro.org>, Jeremy.Linton@....com,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC V2 2/2] cpufreq: cppc: Add support for frequency invariance

Hi,

Do you know of a current platform that would benefit from this, that we
could run some tests on?

I've Cc-ed Jeremy as well, as he might be interested in this.

Also, please find some initial comments below:

On Tuesday 15 Dec 2020 at 16:46:36 (+0530), Viresh Kumar wrote:
> The Frequency Invariance Engine (FIE) is providing a frequency scaling
> correction factor that helps achieve more accurate load-tracking.
> 
> Normally, this scaling factor can be obtained directly with the help of
> the cpufreq drivers as they know the exact frequency the hardware is
> running at. But that isn't the case for CPPC cpufreq driver.
> 
> Another way of obtaining that is using the AMU counter support, which is
> already present in kernel, but that hardware is optional for platforms.
> 
> This patch thus obtains this scaling factor using the existing logic
> present in the cppc driver. Note that the AMUs have higher priority than
> CPPC counters if available, though the CPPC driver doesn't need to have
> any special handling for that.
> 

Probably best to replace "AMU counters" with "architectural counters" as
the use of cppc_cpufreq is not limited to arm64.

> This also exports sched_setattr_nocheck() as the CPPC driver can be
> built as a module.
> 
> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> ---
>  drivers/cpufreq/cppc_cpufreq.c | 140 ++++++++++++++++++++++++++++++++-
>  include/linux/arch_topology.h  |   1 +
>  kernel/sched/core.c            |   1 +
>  3 files changed, 140 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
> index 7cc9bd8568de..a739e20aefd6 100644
> --- a/drivers/cpufreq/cppc_cpufreq.c
> +++ b/drivers/cpufreq/cppc_cpufreq.c
> @@ -10,14 +10,18 @@
>  
>  #define pr_fmt(fmt)	"CPPC Cpufreq:"	fmt
>  
> +#include <linux/arch_topology.h>
>  #include <linux/kernel.h>
>  #include <linux/module.h>
>  #include <linux/delay.h>
>  #include <linux/cpu.h>
>  #include <linux/cpufreq.h>
>  #include <linux/dmi.h>
> +#include <linux/irq_work.h>
> +#include <linux/kthread.h>
>  #include <linux/time.h>
>  #include <linux/vmalloc.h>
> +#include <uapi/linux/sched/types.h>
>  
>  #include <asm/unaligned.h>
>  
> @@ -39,6 +43,15 @@
>  static struct cppc_cpudata **all_cpu_data;
>  static bool boost_supported;
>  
> +struct cppc_freq_invariance {
> +	struct kthread_worker *worker;
> +	struct irq_work irq_work;
> +	struct kthread_work work;
> +	struct cppc_perf_fb_ctrs prev_perf_fb_ctrs;
> +	unsigned int max_freq;
> +};
> +static DEFINE_PER_CPU(struct cppc_freq_invariance, cppc_f_i);
> +
>  struct cppc_workaround_oem_info {
>  	char oem_id[ACPI_OEM_ID_SIZE + 1];
>  	char oem_table_id[ACPI_OEM_TABLE_ID_SIZE + 1];
> @@ -243,7 +256,7 @@ static int cppc_cpufreq_cpu_init(struct cpufreq_policy *policy)
>  	struct cppc_cpudata *cpu_data = all_cpu_data[policy->cpu];
>  	struct cppc_perf_caps *caps = &cpu_data->perf_caps;
>  	unsigned int cpu = policy->cpu;
> -	int ret = 0;
> +	int ret = 0, i;
>  
>  	cpu_data->cpu = cpu;
>  	ret = cppc_get_perf_caps(cpu, caps);
> @@ -300,6 +313,9 @@ static int cppc_cpufreq_cpu_init(struct cpufreq_policy *policy)
>  
>  	cpu_data->cur_policy = policy;
>  
> +	for_each_cpu(i, policy->cpus)
> +		per_cpu(cppc_f_i, i).max_freq = policy->cpuinfo.max_freq;
> +

Is policy->cpuinfo populated at this point?

>  	/*
>  	 * If 'highest_perf' is greater than 'nominal_perf', we assume CPU Boost
>  	 * is supported.
> @@ -374,7 +390,7 @@ static int cppc_cpufreq_set_boost(struct cpufreq_policy *policy, int state)
>  {
>  	struct cppc_cpudata *cpu_data = all_cpu_data[policy->cpu];
>  	struct cppc_perf_caps *caps = &cpu_data->perf_caps;
> -	int ret;
> +	int ret, i;
>  
>  	if (!boost_supported) {
>  		pr_err("BOOST not supported by CPU or firmware\n");
> @@ -389,6 +405,9 @@ static int cppc_cpufreq_set_boost(struct cpufreq_policy *policy, int state)
>  						       caps->nominal_perf);
>  	policy->cpuinfo.max_freq = policy->max;
>  
> +	for_each_cpu(i, policy->related_cpus)
> +		per_cpu(cppc_f_i, i).max_freq = policy->cpuinfo.max_freq;
> +
>  	ret = freq_qos_update_request(policy->max_freq_req, policy->max);
>  	if (ret < 0)
>  		return ret;
> @@ -449,6 +468,120 @@ static void cppc_check_hisi_workaround(void)
>  	acpi_put_table(tbl);
>  }
>  
> +static void cppc_scale_freq_tick_workfn(struct kthread_work *work)
> +{
> +	struct cppc_freq_invariance *cppc_fi;
> +	struct cppc_perf_fb_ctrs fb_ctrs = {0};
> +	int cpu = raw_smp_processor_id();
> +	struct cppc_cpudata *cpudata = all_cpu_data[cpu];
> +	u64 rate;
> +
> +	cppc_fi = container_of(work, struct cppc_freq_invariance, work);
> +
> +	if (cppc_get_perf_ctrs(cpu, &fb_ctrs)) {
> +		pr_info("%s: cppc_get_perf_ctrs() failed\n", __func__);
> +		return;
> +	}
> +
> +	rate = cppc_get_rate_from_fbctrs(cpudata, cppc_fi->prev_perf_fb_ctrs, fb_ctrs);
> +	cppc_fi->prev_perf_fb_ctrs = fb_ctrs;
> +
> +	rate <<= SCHED_CAPACITY_SHIFT;
> +	per_cpu(freq_scale, cpu) = div64_u64(rate, cppc_fi->max_freq);

It will save you some computation by skipping the intermediary frequency
scale transition. For this computation you're obtaining current
performance from counters, on the CPPC abstract performance scale,
then you're converting it to a current frequency, which then gets
translated again to a scale factor on the [0,1024] scale.

You probably want to keep the sanitation done in
cppc_get_rate_from_fbctrs() on the counter values, but you could skip
the call to cppc_cpufreq_perf_to_khz(), and use obtained performance
together with caps->highest_perf, or caps->nominal_perf instead of
cppc_fi->max_freq, in this function.

Also, to optimise it further, you can compute a reference scale (from
reference performance and highest/nominal performance as done in
freq_inv_set_max_ratio() - arch/arm64/kernel/topology.c, and use that
instead in further freq scale computations.

I've resurrected my Juno setup and I'll do further review and testing
tomorrow.

Hope it helps,
Ionela.

> +}
> +
> +static void cppc_irq_work(struct irq_work *irq_work)
> +{
> +	struct cppc_freq_invariance *cppc_fi;
> +
> +	cppc_fi = container_of(irq_work, struct cppc_freq_invariance, irq_work);
> +	kthread_queue_work(cppc_fi->worker, &cppc_fi->work);
> +}
> +
> +static void cppc_scale_freq_tick(void)
> +{
> +	struct cppc_freq_invariance *cppc_fi = &per_cpu(cppc_f_i, raw_smp_processor_id());
> +
> +	/*
> +	 * cppc_get_perf_ctrs() can potentially sleep, call that from the right
> +	 * context.
> +	 */
> +	irq_work_queue(&cppc_fi->irq_work);
> +}
> +
> +static struct scale_freq_tick_data cppc_sftd = {
> +	.source = SCALE_FREQ_SOURCE_CPPC,
> +	.scale_freq = cppc_scale_freq_tick,
> +};
> +
> +static void cppc_freq_invariance_exit(void)
> +{
> +	struct cppc_freq_invariance *cppc_fi;
> +	int i;
> +
> +	if (cppc_cpufreq_driver.get == hisi_cppc_cpufreq_get_rate)
> +		return;
> +
> +	topology_clear_scale_freq_tick(SCALE_FREQ_SOURCE_CPPC, cpu_present_mask);
> +
> +	for_each_possible_cpu(i) {
> +		cppc_fi = &per_cpu(cppc_f_i, i);
> +		if (cppc_fi->worker) {
> +			irq_work_sync(&cppc_fi->irq_work);
> +			kthread_destroy_worker(cppc_fi->worker);
> +			cppc_fi->worker = NULL;
> +		}
> +	}
> +}
> +
> +static void __init cppc_freq_invariance_init(void)
> +{
> +	struct cppc_perf_fb_ctrs fb_ctrs = {0};
> +	struct cppc_freq_invariance *cppc_fi;
> +	struct sched_attr attr = {
> +		.size		= sizeof(struct sched_attr),
> +		.sched_policy	= SCHED_DEADLINE,
> +		.sched_nice	= 0,
> +		.sched_priority	= 0,
> +		/*
> +		 * Fake (unused) bandwidth; workaround to "fix"
> +		 * priority inheritance.
> +		 */
> +		.sched_runtime	= 1000000,
> +		.sched_deadline = 10000000,
> +		.sched_period	= 10000000,
> +	};
> +	struct kthread_worker *worker;
> +	int i, ret;
> +
> +	if (cppc_cpufreq_driver.get == hisi_cppc_cpufreq_get_rate)
> +		return;
> +
> +	for_each_possible_cpu(i) {
> +		cppc_fi = &per_cpu(cppc_f_i, i);
> +
> +		kthread_init_work(&cppc_fi->work, cppc_scale_freq_tick_workfn);
> +		init_irq_work(&cppc_fi->irq_work, cppc_irq_work);
> +		worker = kthread_create_worker_on_cpu(i, 0, "cppc:%d", i);
> +		if (IS_ERR(worker))
> +			return cppc_freq_invariance_exit();
> +
> +		cppc_fi->worker = worker;
> +		ret = sched_setattr_nocheck(worker->task, &attr);
> +		if (ret) {
> +			pr_warn("%s: failed to set SCHED_DEADLINE\n", __func__);
> +			return cppc_freq_invariance_exit();
> +		}
> +
> +		ret = cppc_get_perf_ctrs(i, &fb_ctrs);
> +		if (!ret)
> +			per_cpu(cppc_fi->prev_perf_fb_ctrs, i) = fb_ctrs;
> +	}
> +
> +	/* Register for freq-invariance */
> +	topology_set_scale_freq_tick(&cppc_sftd, cpu_present_mask);
> +}
> +
>  static int __init cppc_cpufreq_init(void)
>  {
>  	struct cppc_cpudata *cpu_data;
> @@ -484,6 +617,8 @@ static int __init cppc_cpufreq_init(void)
>  	if (ret)
>  		goto out;
>  
> +	cppc_freq_invariance_init();
> +
>  	return ret;
>  
>  out:
> @@ -504,6 +639,7 @@ static void __exit cppc_cpufreq_exit(void)
>  	struct cppc_cpudata *cpu_data;
>  	int i;
>  
> +	cppc_freq_invariance_exit();
>  	cpufreq_unregister_driver(&cppc_cpufreq_driver);
>  
>  	for_each_possible_cpu(i) {
> diff --git a/include/linux/arch_topology.h b/include/linux/arch_topology.h
> index b2422ebef2dd..09205b584ca5 100644
> --- a/include/linux/arch_topology.h
> +++ b/include/linux/arch_topology.h
> @@ -36,6 +36,7 @@ bool topology_scale_freq_invariant(void);
>  
>  enum scale_freq_tick_source {
>  	SCALE_FREQ_SOURCE_AMU,
> +	SCALE_FREQ_SOURCE_CPPC,
>  };
>  
>  struct scale_freq_tick_data {
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 51514eef0a9d..76b2fa1a7aaa 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -6075,6 +6075,7 @@ int sched_setattr_nocheck(struct task_struct *p, const struct sched_attr *attr)
>  {
>  	return __sched_setscheduler(p, attr, false, true);
>  }
> +EXPORT_SYMBOL_GPL(sched_setattr_nocheck);
>  
>  /**
>   * sched_setscheduler_nocheck - change the scheduling policy and/or RT priority of a thread from kernelspace.
> -- 
> 2.25.0.rc1.19.g042ed3e048af
> 

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