cpufreq: cppc: Add support for frequency invariance

drivers/base/arch_topology.c +3 -0

index de8587cc119e..07774fb47bc4 100644
@@ -21,17 +21,65 @@
 #include <linux/sched.h>
 #include <linux/smp.h>
 
+static DEFINE_PER_CPU(struct scale_freq_tick_data *, sft_data);
+static struct cpumask scale_freq_tick_mask;
+

drivers/base/arch_topology.c +18 -2

+			per_cpu(sft_data, cpu) = data;
+			cpumask_set_cpu(cpu, &scale_freq_tick_mask);
+		}
+	}
 }
+EXPORT_SYMBOL_GPL(topology_set_scale_freq_tick);
 
-__weak bool arch_freq_counters_available(const struct cpumask *cpus)
+void topology_clear_scale_freq_tick(enum scale_freq_tick_source source,
+				    const struct cpumask *cpus)
 {
-	return false;
+	struct scale_freq_tick_data *sftd;
+	int cpu;
+
+	for_each_cpu(cpu, cpus) {
+		sftd = per_cpu(sft_data, cpu);
+
+		if (sftd && sftd->source == source) {
+			per_cpu(sft_data, cpu) = NULL;
+			cpumask_clear_cpu(cpu, &scale_freq_tick_mask);
+		}
+	}

drivers/base/arch_topology.c +3 -1

+
 DEFINE_PER_CPU(unsigned long, freq_scale) = SCHED_CAPACITY_SCALE;
+EXPORT_SYMBOL_GPL(freq_scale);
 
 void topology_set_freq_scale(const struct cpumask *cpus, unsigned long cur_freq,
 			     unsigned long max_freq)

@@ -47,7 +95,7 @@ void topology_set_freq_scale(const struct cpumask *cpus, unsigned long cur_freq,
 	 * want to update the scale factor with information from CPUFREQ.
 	 * Instead the scale factor will be updated from arch_scale_freq_tick.
 	 */
-	if (arch_freq_counters_available(cpus))
+	if (supports_scale_freq_tick(cpus))
 		return;
 
 	scale = (cur_freq << SCHED_CAPACITY_SHIFT) / max_freq;

include/linux/arch_topology.h +0 -0

index 0f6cd6b73a61..b2422ebef2dd 100644
@@ -34,7 +34,18 @@ void topology_set_freq_scale(const struct cpumask *cpus, unsigned long cur_freq,
 			     unsigned long max_freq);
 bool topology_scale_freq_invariant(void);

include/linux/arch_topology.h +4 -0

+
+void topology_scale_freq_tick(void);
+void topology_set_scale_freq_tick(struct scale_freq_tick_data *data, const struct cpumask *cpus);
+void topology_clear_scale_freq_tick(enum scale_freq_tick_source source, const struct cpumask *cpus);
 
 DECLARE_PER_CPU(unsigned long, thermal_pressure);
 

Signature · 1 line

2.25.0.rc1.19.g042ed3e048af

Review

Quoted 7 lines · Viresh Kumar

(quoted diff) +7 -0

+void topology_scale_freq_tick(void)
+{
+	struct scale_freq_tick_data *sftd = *this_cpu_ptr(&sft_data);
+
+	if (sftd)
+		sftd->scale_freq();
+}

What do you think about having a single topology function that handles all sources of invariance (cpufreq, arch counters, platform counters)?

Quoted 11 lines · Ionela Voinescu

drivers/base/arch_topology.c line 79

Quoted 7 lines · Viresh Kumar

drivers/base/arch_topology.c +7 -0

+void topology_scale_freq_tick(void)
+{
+	struct scale_freq_tick_data *sftd = *this_cpu_ptr(&sft_data);
+
+	if (sftd)
+		sftd->scale_freq();
+}

What do you think about having a single topology function that handles all sources of invariance (cpufreq, arch counters, platform counters)?

I think keeping them separate is better, both of these are called from scheduler's context (hotpath) and adding any more unnecessary conditionals there should be rather avoided. We could have given a

though to merging them if they were going to share some code, but that is not the case here clearly. They are quite different.

This is how it looks now:

arch/arm64/include/asm/topology.h +0 -0

index 3b8dca4eb08d..be6a53ba3e2d 100644
@@ -17,15 +17,9 @@ int pcibus_to_node(struct pci_bus *bus);
 #include <linux/arch_topology.h>
 

arch/arm64/include/asm/topology.h +0 -1

-#endif /* CONFIG_ARM64_AMU_EXTN */
 
 /* Replace task scheduler's default frequency-invariant accounting */
 #define arch_set_freq_scale topology_set_freq_scale

arch/arm64/kernel/topology.c +39 -50

index e08a4126453a..1e47dfd465f8 100644
@@ -199,8 +199,44 @@ static int freq_inv_set_max_ratio(int cpu, u64 max_rate, u64 ref_rate)
 	return 0;
 }
 
-static DEFINE_STATIC_KEY_FALSE(amu_fie_key);
-#define amu_freq_invariant() static_branch_unlikely(&amu_fie_key)
+static void amu_scale_freq_tick(void)
+{
+	u64 prev_core_cnt, prev_const_cnt;
+	u64 core_cnt, const_cnt, scale;
+
+	prev_const_cnt = this_cpu_read(arch_const_cycles_prev);
+	prev_core_cnt = this_cpu_read(arch_core_cycles_prev);
+
+	update_freq_counters_refs();
+
+	const_cnt = this_cpu_read(arch_const_cycles_prev);
+	core_cnt = this_cpu_read(arch_core_cycles_prev);
+
+	if (unlikely(core_cnt <= prev_core_cnt ||
+		     const_cnt <= prev_const_cnt))
+		return;
+
+	/*
+	 *	    /\core    arch_max_freq_scale
+	 * scale =  ------- * --------------------
+	 *	    /\const   SCHED_CAPACITY_SCALE
+	 *
+	 * See validate_cpu_freq_invariance_counters() for details on
+	 * arch_max_freq_scale and the use of SCHED_CAPACITY_SHIFT.
+	 */
+	scale = core_cnt - prev_core_cnt;
+	scale *= this_cpu_read(arch_max_freq_scale);
+	scale = div64_u64(scale >> SCHED_CAPACITY_SHIFT,
+			  const_cnt - prev_const_cnt);
+
+	scale = min_t(unsigned long, scale, SCHED_CAPACITY_SCALE);
+	this_cpu_write(freq_scale, (unsigned long)scale);
+}
+
+static struct scale_freq_data amu_sfd = {
+	.source = SCALE_FREQ_SOURCE_ARCH,
+	.set_freq_scale = amu_scale_freq_tick,
+};
 
 static void amu_fie_setup(const struct cpumask *cpus)
 {

@@ -227,7 +263,7 @@ static void amu_fie_setup(const struct cpumask *cpus)
 	if (!invariant && !cpumask_equal(amu_fie_cpus, cpu_present_mask))
 		return;
 
-	static_branch_enable(&amu_fie_key);
+	topology_set_scale_freq_source(&amu_sfd, amu_fie_cpus);
 
 	pr_debug("CPUs[%*pbl]: counters will be used for FIE.",
 		 cpumask_pr_args(cpus));

@@ -283,53 +319,6 @@ static int __init init_amu_fie(void)
 }
 core_initcall(init_amu_fie);
 
-bool arch_freq_counters_available(const struct cpumask *cpus)
-{
-	return amu_freq_invariant() &&
-	       cpumask_subset(cpus, amu_fie_cpus);
-}
-
-void topology_scale_freq_tick(void)
-{
-	u64 prev_core_cnt, prev_const_cnt;
-	u64 core_cnt, const_cnt, scale;
-	int cpu = smp_processor_id();
-
-	if (!amu_freq_invariant())
-		return;
-
-	if (!cpumask_test_cpu(cpu, amu_fie_cpus))
-		return;
-
-	prev_const_cnt = this_cpu_read(arch_const_cycles_prev);
-	prev_core_cnt = this_cpu_read(arch_core_cycles_prev);
-
-	update_freq_counters_refs();
-
-	const_cnt = this_cpu_read(arch_const_cycles_prev);
-	core_cnt = this_cpu_read(arch_core_cycles_prev);
-
-	if (unlikely(core_cnt <= prev_core_cnt ||
-		     const_cnt <= prev_const_cnt))
-		return;
-
-	/*
-	 *	    /\core    arch_max_freq_scale
-	 * scale =  ------- * --------------------
-	 *	    /\const   SCHED_CAPACITY_SCALE
-	 *
-	 * See validate_cpu_freq_invariance_counters() for details on
-	 * arch_max_freq_scale and the use of SCHED_CAPACITY_SHIFT.
-	 */
-	scale = core_cnt - prev_core_cnt;
-	scale *= this_cpu_read(arch_max_freq_scale);
-	scale = div64_u64(scale >> SCHED_CAPACITY_SHIFT,
-			  const_cnt - prev_const_cnt);
-
-	scale = min_t(unsigned long, scale, SCHED_CAPACITY_SCALE);
-	this_cpu_write(freq_scale, (unsigned long)scale);
-}
-
 #ifdef CONFIG_ACPI_CPPC_LIB
 #include <acpi/cppc_acpi.h>
 

drivers/base/arch_topology.c +52 -4

index de8587cc119e..e2115ea348dc 100644
@@ -21,17 +21,65 @@
 #include <linux/sched.h>
 #include <linux/smp.h>
 
+static DEFINE_PER_CPU(struct scale_freq_data *, sft_data);
+static struct cpumask scale_freq_counters_mask;
+
+static bool supports_scale_freq_counters(const struct cpumask *cpus)
+{
+	return cpumask_subset(cpus, &scale_freq_counters_mask);
+}
+
 bool topology_scale_freq_invariant(void)
 {
 	return cpufreq_supports_freq_invariance() ||
-	       arch_freq_counters_available(cpu_online_mask);
+	       supports_scale_freq_counters(cpu_online_mask);
+}
+
+void topology_set_scale_freq_source(struct scale_freq_data *data,
+				  const struct cpumask *cpus)
+{
+	struct scale_freq_data *sfd;
+	int cpu;
+
+	for_each_cpu(cpu, cpus) {
+		sfd = per_cpu(sft_data, cpu);
+
+		/* Use ARCH provided counters whenever possible */
+		if (!sfd || sfd->source != SCALE_FREQ_SOURCE_ARCH) {
+			per_cpu(sft_data, cpu) = data;
+			cpumask_set_cpu(cpu, &scale_freq_counters_mask);
+		}
+	}
 }
+EXPORT_SYMBOL_GPL(topology_set_scale_freq_source);
 
-__weak bool arch_freq_counters_available(const struct cpumask *cpus)
+void topology_clear_scale_freq_source(enum scale_freq_source source,
+				    const struct cpumask *cpus)
 {
-	return false;
+	struct scale_freq_data *sfd;
+	int cpu;
+
+	for_each_cpu(cpu, cpus) {
+		sfd = per_cpu(sft_data, cpu);
+
+		if (sfd && sfd->source == source) {
+			per_cpu(sft_data, cpu) = NULL;
+			cpumask_clear_cpu(cpu, &scale_freq_counters_mask);
+		}
+	}
 }
+EXPORT_SYMBOL_GPL(topology_clear_scale_freq_source);
+
+void topology_scale_freq_tick(void)
+{
+	struct scale_freq_data *sfd = *this_cpu_ptr(&sft_data);
+
+	if (sfd)
+		sfd->set_freq_scale();
+}
+
 DEFINE_PER_CPU(unsigned long, freq_scale) = SCHED_CAPACITY_SCALE;
+EXPORT_SYMBOL_GPL(freq_scale);
 
 void topology_set_freq_scale(const struct cpumask *cpus, unsigned long cur_freq,
 			     unsigned long max_freq)

@@ -47,7 +95,7 @@ void topology_set_freq_scale(const struct cpumask *cpus, unsigned long cur_freq,
 	 * want to update the scale factor with information from CPUFREQ.
 	 * Instead the scale factor will be updated from arch_scale_freq_tick.
 	 */
-	if (arch_freq_counters_available(cpus))
+	if (supports_scale_freq_counters(cpus))
 		return;
 
 	scale = (cur_freq << SCHED_CAPACITY_SHIFT) / max_freq;

include/linux/arch_topology.h +0 -0

index 0f6cd6b73a61..1bcbf8eff991 100644

include/linux/arch_topology.h +4 -0

+	SCALE_FREQ_SOURCE_ARCH,
+};
+
+struct scale_freq_data {

Signature · 2 lines

-- 
viresh

I think it would improve clarity a lot by having a single topology function, with clear comments on which path is taken when.

In regards to them sharing code, there's not much code they could be sharing, as one just does some simple math on provided values. I attempted to have a single function for frequency invariance at some point [1], as the logic for the computation is the same, but I could never convince myself the clarity gained was worth the changes. But I really like this version of your code for this purpose as well.

But I'll leave that to your judgement.

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.

This also exports sched_setattr_nocheck() as the CPPC driver can be built as a module.

Signed-off-by Viresh Kumar <[email protected]>

---
 drivers/cpufreq/cppc_cpufreq.c | 140 ++++++++++++++++++++++++++++++++-
 include/linux/arch_topology.h  |   1 +
 kernel/sched/core.c            |   1 +
 3 files changed, 140 insertions(+), 2 deletions(-)

drivers/cpufreq/cppc_cpufreq.c +14 -1

index 7cc9bd8568de..a739e20aefd6 100644
@@ -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);

drivers/cpufreq/cppc_cpufreq.c +14 -1

 	/*
 	 * 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);
+

drivers/cpufreq/cppc_cpufreq.c +97 -0

+}
+
+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) {

include/linux/arch_topology.h +1 -0

index b2422ebef2dd..09205b584ca5 100644
@@ -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 {

kernel/sched/core.c +1 -0

index 51514eef0a9d..76b2fa1a7aaa 100644
@@ -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.

Signature · 1 line

2.25.0.rc1.19.g042ed3e048af

Hi,

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

Quoted 11 lines

(quoted diff) +1 -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)
 

Review static int cppc_cpufreq_cpu_init(struct cpufreq_policy *policy) · line 318

Quoted 5 lines

(quoted diff) +3 -0

 	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?

Quoted 10 lines

(quoted diff) +10 -0

+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);
+

Review static int cppc_cpufreq_cpu_init(struct cpufreq_policy *policy)

Quoted 10 lines

(quoted diff) +10 -0

+	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.

Hello,

CPPC cpufreq driver is used for ARM servers and this patch series tries to provide frequency invariance support for them.

This is tested with some hacks, as I didn't have access to the right hardware, on the ARM64 hikey board to check the overall functionality and that works fine.

Ionela/Peter Puhov, it would be nice if you guys can give this a shot.

This is based of pm/linux-next and patches [1] and [2] which I sent recently to cleanup arm64 topology stuff.

Changes since V1:
- The interface for setting the callbacks is improved, so different parts looking to provide their callbacks don't need to think about each other.

- Moved to per-cpu storage for storing the callback related data, AMU counters have higher priority with this.

--
viresh

[1] https://lore.kernel.org/lkml/7a171f710cdc0f808a2bfbd7db839c0d265527e7.1607579234.git.viresh.kumar@linaro.org/
[2] https://lore.kernel.org/lkml/5ffc7b9ed03c6301ac2f710f609282959491b526.1608010334.git.viresh.kumar@linaro.org/

Viresh Kumar (2):
topology: Allow multiple entities to provide sched_freq_tick()
callback
cpufreq: cppc: Add support for frequency invariance

 arch/arm64/include/asm/topology.h |   8 +-
 arch/arm64/kernel/topology.c      |  89 +++++++++----------
 drivers/base/arch_topology.c      |  56 +++++++++++-
 drivers/cpufreq/cppc_cpufreq.c    | 140 +++++++++++++++++++++++++++++-
 include/linux/arch_topology.h     |  14 ++-
 kernel/sched/core.c               |   1 +
 6 files changed, 244 insertions(+), 64 deletions(-)

Signature · 1 line

2.25.0.rc1.19.g042ed3e048af