[PATCH v8 0/4] Add support for AArch64 AMUv1-based average freq

[PATCH v8 0/4] Add support for AArch64 AMUv1-based average freq

[Beata Michalska]

Hi All,

This series adds support for obtaining an average CPU frequency based on
a hardware provided feedback. The average frequency is being exposed via
dedicated yet optional cpufreq sysfs attribute - cpuinfo_avg_freq.
The architecture specific bits are being provided for AArch64, caching on
existing implementation for FIE and AMUv1 support: the frequency scale
factor, updated on each sched tick, serving as a base for retrieving
the frequency for a given CPU, representing an average frequency
reported between the ticks.

The changes have been rather lightly (due to some limitations) tested on
an FVP model.

Note that [PATCH 2/4] arm64: amu: Delay allocating cpumask for AMU FIE support
can be merged independently.
Additionally, this series depends on [6]

Relevant discussions:
[1] https://lore.kernel.org/all/20240229162520.970986-1-vanshikonda@os.amperecomputing.com/
[2] https://lore.kernel.org/all/7eozim2xnepacnnkzxlbx34hib4otycnbn4dqymfziqou5lw5u@5xzpv3t7sxo3/
[3] https://lore.kernel.org/all/20231212072617.14756-1-lihuisong@huawei.com/
[4] https://lore.kernel.org/lkml/ZIHpd6unkOtYVEqP@e120325.cambridge.arm.com/T/#m4e74cb5a0aaa353c60fedc6cfb95ab7a6e381e3c
[5] https://lore.kernel.org/all/20240603081331.3829278-1-beata.michalska@arm.com/
[6] https://lore.kernel.org/all/20240827154818.1195849-1-ionela.voinescu@arm.com/

v8:
- Drop introducing new function and reuse arch_freq_get_on_cpu, guarding its use
  in scaling_cur_freq sysfs handler with dedicated config for x86

v7:
- Dropping 'arch_topology: init capacity_freq_ref to 0' patch from the series
  as this one has been sent separately as an independent change
  [https://lore.kernel.org/all/20240827154818.1195849-1-ionela.voinescu@arm.com/]
- Including in the series change that introduces new sysfs entry [PATCH 1/4]
- Consequently modifying previously arch_freq_get_on_cpu to match reqs for new
  sysfs attribute
- Dropping an idea of considering a CPU that has been idle for a while as a
  valid source of information for obtaining an AMU-counter based frequency
- Some minor cosmetic changes

v6:
 - delay allocating cpumask for AMU FIE support instead of invalidating the mask
   upon failure to register cpufreq policy notifications
 - drop the change to cpufreq core (for cpuinfo_cur_freq) as this one will be
   sent as a separate change

v5:
 - Fix invalid access to cpumask
 - Reworked finding reference cpu when getting the freq

v4:
- dropping seqcount
- fixing identifying active cpu within given policy
- skipping full dynticks cpus when retrieving the freq
- bringing back plugging in arch_freq_get_on_cpu into cpuinfo_cur_freq

v3:
- dropping changes to cpufreq_verify_current_freq
- pulling in changes from Ionela initializing capacity_freq_ref to 0
  (thanks for that!)  and applying suggestions made by her during last review:
	- switching to arch_scale_freq_capacity and arch_scale_freq_ref when
	  reversing freq scale factor computation
	- swapping shift with multiplication
- adding time limit for considering last scale update as valid
- updating frequency scale factor upon entering idle

v2:
- Splitting the patches
- Adding comment for full dyntick mode
- Plugging arch_freq_get_on_cpu into cpufreq_verify_current_freq instead
  of in show_cpuinfo_cur_freq to allow the framework to stay more in sync
  with potential freq changes

CC: Jonathan Corbet <corbet@lwn.net>
CC: Thomas Gleixner <tglx@linutronix.de>
CC: Ingo Molnar <mingo@redhat.com>
CC: Borislav Petkov <bp@alien8.de>
CC: Dave Hansen <dave.hansen@linux.intel.com>
CC: H. Peter Anvin <hpa@zytor.com>
CC: Phil Auld <pauld@redhat.com>
CC: x86@kernel.org
CC: linux-doc@vger.kernel.org

Beata Michalska (4):
  cpufreq: Introduce an optional cpuinfo_avg_freq sysfs entry
  arm64: amu: Delay allocating cpumask for AMU FIE support
  arm64: Provide an AMU-based version of arch_freq_get_on_cpu
  arm64: Update AMU-based freq scale factor on entering idle

 Documentation/admin-guide/pm/cpufreq.rst |  16 ++-
 arch/arm64/kernel/topology.c             | 144 +++++++++++++++++++----
 arch/x86/kernel/cpu/aperfmperf.c         |   2 +-
 arch/x86/kernel/cpu/proc.c               |   7 +-
 drivers/cpufreq/Kconfig.x86              |  12 ++
 drivers/cpufreq/cpufreq.c                |  36 +++++-
 include/linux/cpufreq.h                  |   2 +-
 7 files changed, 188 insertions(+), 31 deletions(-)

-- 
2.25.1

[PATCH v8 1/4] cpufreq: Introduce an optional cpuinfo_avg_freq sysfs entry

[Beata Michalska]

Currently the CPUFreq core exposes two sysfs attributes that can be used
to query current frequency of a given CPU(s): namely cpuinfo_cur_freq
and scaling_cur_freq. Both provide slightly different view on the
subject and they do come with their own drawbacks.

cpuinfo_cur_freq provides higher precision though at a cost of being
rather expensive. Moreover, the information retrieved via this attribute
is somewhat short lived as frequency can change at any point of time
making it difficult to reason from.

scaling_cur_freq, on the other hand, tends to be less accurate but then
the actual level of precision (and source of information) varies between
architectures making it a bit ambiguous.

The new attribute, cpuinfo_avg_freq, is intended to provide more stable,
distinct interface, exposing an average frequency of a given CPU(s), as
reported by the hardware, over a time frame spanning no more than a few
milliseconds. As it requires appropriate hardware support, this
interface is optional.

Note that under the hood, the new attribute relies on the information
provided by arch_freq_get_on_cpu, which, up to this point, has been
feeding data for scaling_cur_freq attribute, being the source of
ambiguity when it comes to interpretation. This has been amended by
restoring the intended behavior for scaling_cur_freq, with a new
dedicated config option to maintain status quo for those, who may need
it.

CC: Jonathan Corbet <corbet@lwn.net>
CC: Thomas Gleixner <tglx@linutronix.de>
CC: Ingo Molnar <mingo@redhat.com>
CC: Borislav Petkov <bp@alien8.de>
CC: Dave Hansen <dave.hansen@linux.intel.com>
CC: H. Peter Anvin <hpa@zytor.com>
CC: Phil Auld <pauld@redhat.com>
CC: x86@kernel.org
CC: linux-doc@vger.kernel.org
Signed-off-by: Beata Michalska <beata.michalska@arm.com>
---
 Documentation/admin-guide/pm/cpufreq.rst | 16 ++++++++++-
 arch/x86/kernel/cpu/aperfmperf.c         |  2 +-
 arch/x86/kernel/cpu/proc.c               |  7 +++--
 drivers/cpufreq/Kconfig.x86              | 12 ++++++++
 drivers/cpufreq/cpufreq.c                | 36 +++++++++++++++++++++---
 include/linux/cpufreq.h                  |  2 +-
 6 files changed, 66 insertions(+), 9 deletions(-)

diff --git a/Documentation/admin-guide/pm/cpufreq.rst b/Documentation/admin-guide/pm/cpufreq.rst
index fe1be4ad88cb..76f3835afe01 100644
--- a/Documentation/admin-guide/pm/cpufreq.rst
+++ b/Documentation/admin-guide/pm/cpufreq.rst
@@ -248,6 +248,19 @@ are the following:
 	If that frequency cannot be determined, this attribute should not
 	be present.
 
+``cpuinfo_avg_freq``
+        An average frequency (in KHz) of all CPUs belonging to a given policy,
+        derived from a hardware provided feedback and reported on a time frame
+        spanning at most few milliseconds.
+
+        This is expected to be based on the frequency the hardware actually runs
+        at and, as such, might require specialised hardware support (such as AMU
+        extension on ARM). If one cannot be determined, this attribute should
+        not be present.
+
+        Note, that failed attempt to retrieve current frequency for a given
+        CPU(s) will result in an appropriate error.
+
 ``cpuinfo_max_freq``
 	Maximum possible operating frequency the CPUs belonging to this policy
 	can run at (in kHz).
@@ -293,7 +306,8 @@ are the following:
 	Some architectures (e.g. ``x86``) may attempt to provide information
 	more precisely reflecting the current CPU frequency through this
 	attribute, but that still may not be the exact current CPU frequency as
-	seen by the hardware at the moment.
+	seen by the hardware at the moment. This behavior though, is only
+	available via c:macro:``CPUFREQ_ARCH_CUR_FREQ`` option.
 
 ``scaling_driver``
 	The scaling driver currently in use.
diff --git a/arch/x86/kernel/cpu/aperfmperf.c b/arch/x86/kernel/cpu/aperfmperf.c
index 0b69bfbf345d..a00059139ca4 100644
--- a/arch/x86/kernel/cpu/aperfmperf.c
+++ b/arch/x86/kernel/cpu/aperfmperf.c
@@ -413,7 +413,7 @@ void arch_scale_freq_tick(void)
  */
 #define MAX_SAMPLE_AGE	((unsigned long)HZ / 50)
 
-unsigned int arch_freq_get_on_cpu(int cpu)
+int arch_freq_get_on_cpu(int cpu)
 {
 	struct aperfmperf *s = per_cpu_ptr(&cpu_samples, cpu);
 	unsigned int seq, freq;
diff --git a/arch/x86/kernel/cpu/proc.c b/arch/x86/kernel/cpu/proc.c
index e65fae63660e..34d8fb93fb70 100644
--- a/arch/x86/kernel/cpu/proc.c
+++ b/arch/x86/kernel/cpu/proc.c
@@ -86,9 +86,12 @@ static int show_cpuinfo(struct seq_file *m, void *v)
 		seq_printf(m, "microcode\t: 0x%x\n", c->microcode);
 
 	if (cpu_has(c, X86_FEATURE_TSC)) {
-		unsigned int freq = arch_freq_get_on_cpu(cpu);
+		int freq = arch_freq_get_on_cpu(cpu);
 
-		seq_printf(m, "cpu MHz\t\t: %u.%03u\n", freq / 1000, (freq % 1000));
+		if (freq <= 0)
+			seq_puts(m, "cpu MHz\t\t: Unknown\n");
+		else
+			seq_printf(m, "cpu MHz\t\t: %u.%03u\n", freq / 1000, (freq % 1000));
 	}
 
 	/* Cache size */
diff --git a/drivers/cpufreq/Kconfig.x86 b/drivers/cpufreq/Kconfig.x86
index 97c2d4f15d76..212e1b9afe21 100644
--- a/drivers/cpufreq/Kconfig.x86
+++ b/drivers/cpufreq/Kconfig.x86
@@ -340,3 +340,15 @@ config X86_SPEEDSTEP_RELAXED_CAP_CHECK
 	  option lets the probing code bypass some of those checks if the
 	  parameter "relaxed_check=1" is passed to the module.
 
+config CPUFREQ_ARCH_CUR_FREQ
+	default y
+	bool "Current frequency derived from HW provided feedback"
+	help
+	  This determines whether the scaling_cur_freq sysfs attribute returns
+	  the last requested frequency or a more precise value based on hardware
+	  provided feedback (as architected counters).
+	  Given that a more precise frequency can now be provided via the
+	  cpuinfo_avg_cur_freq attribute, by enabling this option,
+	  scaling_cur_freq maintains the provision of a counter based frequency,
+	  for compatibility reasons.
+
diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 04fc786dd2c0..70df2a24437b 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -747,9 +747,14 @@ show_one(cpuinfo_transition_latency, cpuinfo.transition_latency);
 show_one(scaling_min_freq, min);
 show_one(scaling_max_freq, max);
 
-__weak unsigned int arch_freq_get_on_cpu(int cpu)
+__weak int arch_freq_get_on_cpu(int cpu)
 {
-	return 0;
+	return -EOPNOTSUPP;
+}
+
+static inline bool cpufreq_avg_freq_supported(struct cpufreq_policy *policy)
+{
+	return arch_freq_get_on_cpu(policy->cpu) != -EOPNOTSUPP;
 }
 
 static ssize_t show_scaling_cur_freq(struct cpufreq_policy *policy, char *buf)
@@ -757,8 +762,11 @@ static ssize_t show_scaling_cur_freq(struct cpufreq_policy *policy, char *buf)
 	ssize_t ret;
 	unsigned int freq;
 
-	freq = arch_freq_get_on_cpu(policy->cpu);
-	if (freq)
+	freq = IS_ENABLED(CONFIG_CPUFREQ_ARCH_CUR_FREQ)
+		? arch_freq_get_on_cpu(policy->cpu)
+		: 0;
+
+	if (freq > 0)
 		ret = sysfs_emit(buf, "%u\n", freq);
 	else if (cpufreq_driver->setpolicy && cpufreq_driver->get)
 		ret = sysfs_emit(buf, "%u\n", cpufreq_driver->get(policy->cpu));
@@ -802,6 +810,19 @@ static ssize_t show_cpuinfo_cur_freq(struct cpufreq_policy *policy,
 	return sysfs_emit(buf, "<unknown>\n");
 }
 
+/*
+ * show_cpuinfo_avg_freq - average CPU frequency as detected by hardware
+ */
+static ssize_t show_cpuinfo_avg_freq(struct cpufreq_policy *policy,
+				     char *buf)
+{
+	int avg_freq = arch_freq_get_on_cpu(policy->cpu);
+
+	if (avg_freq > 0)
+		return sysfs_emit(buf, "%u\n", avg_freq);
+	return avg_freq != 0 ? avg_freq : -EINVAL;
+}
+
 /*
  * show_scaling_governor - show the current policy for the specified CPU
  */
@@ -964,6 +985,7 @@ static ssize_t show_bios_limit(struct cpufreq_policy *policy, char *buf)
 }
 
 cpufreq_freq_attr_ro_perm(cpuinfo_cur_freq, 0400);
+cpufreq_freq_attr_ro(cpuinfo_avg_freq);
 cpufreq_freq_attr_ro(cpuinfo_min_freq);
 cpufreq_freq_attr_ro(cpuinfo_max_freq);
 cpufreq_freq_attr_ro(cpuinfo_transition_latency);
@@ -1091,6 +1113,12 @@ static int cpufreq_add_dev_interface(struct cpufreq_policy *policy)
 			return ret;
 	}
 
+	if (cpufreq_avg_freq_supported(policy)) {
+		ret = sysfs_create_file(&policy->kobj, &cpuinfo_avg_freq.attr);
+		if (ret)
+			return ret;
+	}
+
 	ret = sysfs_create_file(&policy->kobj, &scaling_cur_freq.attr);
 	if (ret)
 		return ret;
diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
index d4d2f4d1d7cb..a7b6c0ccf9bc 100644
--- a/include/linux/cpufreq.h
+++ b/include/linux/cpufreq.h
@@ -1194,7 +1194,7 @@ static inline int of_perf_domain_get_sharing_cpumask(int pcpu, const char *list_
 }
 #endif
 
-extern unsigned int arch_freq_get_on_cpu(int cpu);
+extern int arch_freq_get_on_cpu(int cpu);
 
 #ifndef arch_set_freq_scale
 static __always_inline
-- 
2.25.1

Re: [PATCH v8 1/4] cpufreq: Introduce an optional cpuinfo_avg_freq sysfs entry

[Viresh Kumar]

On 06-12-24, 13:55, Beata Michalska wrote:
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 04fc786dd2c0..70df2a24437b 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -747,9 +747,14 @@ show_one(cpuinfo_transition_latency, cpuinfo.transition_latency);
>  show_one(scaling_min_freq, min);
>  show_one(scaling_max_freq, max);
>  
> -__weak unsigned int arch_freq_get_on_cpu(int cpu)
> +__weak int arch_freq_get_on_cpu(int cpu)
>  {
> -	return 0;
> +	return -EOPNOTSUPP;

I did suggest not doing this as it may not be acceptable.

https://lore.kernel.org/all/CAKohpokFUpQyHYO017kOn-Jbt0CFZ1GuxoG3N-fenWJ_poW=4Q@mail.gmail.com/

-- 
viresh

Re: [PATCH v8 1/4] cpufreq: Introduce an optional cpuinfo_avg_freq sysfs entry

[Beata Michalska]

On Thu, Dec 12, 2024 at 12:21:00PM +0530, Viresh Kumar wrote:
> On 06-12-24, 13:55, Beata Michalska wrote:
> > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> > index 04fc786dd2c0..70df2a24437b 100644
> > --- a/drivers/cpufreq/cpufreq.c
> > +++ b/drivers/cpufreq/cpufreq.c
> > @@ -747,9 +747,14 @@ show_one(cpuinfo_transition_latency, cpuinfo.transition_latency);
> >  show_one(scaling_min_freq, min);
> >  show_one(scaling_max_freq, max);
> >  
> > -__weak unsigned int arch_freq_get_on_cpu(int cpu)
> > +__weak int arch_freq_get_on_cpu(int cpu)
> >  {
> > -	return 0;
> > +	return -EOPNOTSUPP;
> 
> I did suggest not doing this as it may not be acceptable.
> 
> https://lore.kernel.org/all/CAKohpokFUpQyHYO017kOn-Jbt0CFZ1GuxoG3N-fenWJ_poW=4Q@mail.gmail.com/
>
My bad as I must have misinterpreted that message. Although I am not entirely
sure why this might be unacceptable as it is not such uncommon approach to use
signed int space to cover both: expected positive value as well as potential
error code case failure.
Enabling the new attribute for all is an option, tough not entirely compelling
one as exposing a feature that is known not to be supported seems bit
counterintuitive. On the other hand using cpufreq driver flags won't help much
as the support for the new attrib is platform-specific, not driver-specific.

---
BR
Beata
> -- 
> viresh

Re: [PATCH v8 1/4] cpufreq: Introduce an optional cpuinfo_avg_freq sysfs entry

[Viresh Kumar]

On 16-12-24, 23:15, Beata Michalska wrote:
> My bad as I must have misinterpreted that message. Although I am not entirely
> sure why this might be unacceptable as it is not such uncommon approach to use
> signed int space to cover both: expected positive value as well as potential
> error code case failure.

This part is fine. The problem is with handling frequency here. Signed int can
capture up to 2 GHz of freq, where as unsigned int can capture up to 4 GHz and
so we would really like to keep it at 4 GHz..

Maybe we need to move to 64 bits for frequency at some point of time, but at
least we should try to not break it for now.

> Enabling the new attribute for all is an option, tough not entirely compelling
> one as exposing a feature that is known not to be supported seems bit
> counterintuitive. On the other hand using cpufreq driver flags won't help much
> as the support for the new attrib is platform-specific, not driver-specific.

-- 
viresh

Re: [PATCH v8 1/4] cpufreq: Introduce an optional cpuinfo_avg_freq sysfs entry

[Beata Michalska]

On Tue, Dec 17, 2024 at 09:57:26AM +0530, Viresh Kumar wrote:
> On 16-12-24, 23:15, Beata Michalska wrote:
> > My bad as I must have misinterpreted that message. Although I am not entirely
> > sure why this might be unacceptable as it is not such uncommon approach to use
> > signed int space to cover both: expected positive value as well as potential
> > error code case failure.
> 
> This part is fine. The problem is with handling frequency here. Signed int can
> capture up to 2 GHz of freq, where as unsigned int can capture up to 4 GHz and
> so we would really like to keep it at 4 GHz..
Right, though the arch_freq_get_on_cpu operates on kHz values.

---
BR
Beata
> 
> Maybe we need to move to 64 bits for frequency at some point of time, but at
> least we should try to not break it for now.
> 
> > Enabling the new attribute for all is an option, tough not entirely compelling
> > one as exposing a feature that is known not to be supported seems bit
> > counterintuitive. On the other hand using cpufreq driver flags won't help much
> > as the support for the new attrib is platform-specific, not driver-specific.
> 
> -- 
> viresh

Re: [PATCH v8 1/4] cpufreq: Introduce an optional cpuinfo_avg_freq sysfs entry

[Viresh Kumar]

On 17-12-24, 21:10, Beata Michalska wrote:
> On Tue, Dec 17, 2024 at 09:57:26AM +0530, Viresh Kumar wrote:
> > On 16-12-24, 23:15, Beata Michalska wrote:
> > > My bad as I must have misinterpreted that message. Although I am not entirely
> > > sure why this might be unacceptable as it is not such uncommon approach to use
> > > signed int space to cover both: expected positive value as well as potential
> > > error code case failure.
> > 
> > This part is fine. The problem is with handling frequency here. Signed int can
> > capture up to 2 GHz of freq, where as unsigned int can capture up to 4 GHz and
> > so we would really like to keep it at 4 GHz..
> Right, though the arch_freq_get_on_cpu operates on kHz values.

Hmm.. Missed that.

If you still want to keep it, make that change in a separate patch and
the new sysfs entry in a different one, so related people can easily
review.

-- 
viresh

Re: [PATCH v8 1/4] cpufreq: Introduce an optional cpuinfo_avg_freq sysfs entry

[Beata Michalska]

On Wed, Dec 18, 2024 at 09:41:27AM +0530, Viresh Kumar wrote:
> On 17-12-24, 21:10, Beata Michalska wrote:
> > On Tue, Dec 17, 2024 at 09:57:26AM +0530, Viresh Kumar wrote:
> > > On 16-12-24, 23:15, Beata Michalska wrote:
> > > > My bad as I must have misinterpreted that message. Although I am not entirely
> > > > sure why this might be unacceptable as it is not such uncommon approach to use
> > > > signed int space to cover both: expected positive value as well as potential
> > > > error code case failure.
> > > 
> > > This part is fine. The problem is with handling frequency here. Signed int can
> > > capture up to 2 GHz of freq, where as unsigned int can capture up to 4 GHz and
> > > so we would really like to keep it at 4 GHz..
> > Right, though the arch_freq_get_on_cpu operates on kHz values.
> 
> Hmm.. Missed that.
> 
> If you still want to keep it, make that change in a separate patch and
> the new sysfs entry in a different one, so related people can easily
> review.
> 
Will do.
Thank you for your feedback. Much appreciated.

---
BR
Beata

> -- 
> viresh

Re: [PATCH v8 1/4] cpufreq: Introduce an optional cpuinfo_avg_freq sysfs entry

[Kai-Heng Feng]

Hi Beata,

On 2024/12/6 9:55 PM, Beata Michalska wrote:
> Currently the CPUFreq core exposes two sysfs attributes that can be used
> to query current frequency of a given CPU(s): namely cpuinfo_cur_freq
> and scaling_cur_freq. Both provide slightly different view on the
> subject and they do come with their own drawbacks.
> 
> cpuinfo_cur_freq provides higher precision though at a cost of being
> rather expensive. Moreover, the information retrieved via this attribute
> is somewhat short lived as frequency can change at any point of time
> making it difficult to reason from.
> 
> scaling_cur_freq, on the other hand, tends to be less accurate but then
> the actual level of precision (and source of information) varies between
> architectures making it a bit ambiguous.
> 
> The new attribute, cpuinfo_avg_freq, is intended to provide more stable,
> distinct interface, exposing an average frequency of a given CPU(s), as
> reported by the hardware, over a time frame spanning no more than a few
> milliseconds. As it requires appropriate hardware support, this
> interface is optional.
> 
> Note that under the hood, the new attribute relies on the information
> provided by arch_freq_get_on_cpu, which, up to this point, has been
> feeding data for scaling_cur_freq attribute, being the source of
> ambiguity when it comes to interpretation. This has been amended by
> restoring the intended behavior for scaling_cur_freq, with a new
> dedicated config option to maintain status quo for those, who may need
> it.
> 
> CC: Jonathan Corbet <corbet@lwn.net>
> CC: Thomas Gleixner <tglx@linutronix.de>
> CC: Ingo Molnar <mingo@redhat.com>
> CC: Borislav Petkov <bp@alien8.de>
> CC: Dave Hansen <dave.hansen@linux.intel.com>
> CC: H. Peter Anvin <hpa@zytor.com>
> CC: Phil Auld <pauld@redhat.com>
> CC: x86@kernel.org
> CC: linux-doc@vger.kernel.org
> Signed-off-by: Beata Michalska <beata.michalska@arm.com>
> ---
>   Documentation/admin-guide/pm/cpufreq.rst | 16 ++++++++++-
>   arch/x86/kernel/cpu/aperfmperf.c         |  2 +-
>   arch/x86/kernel/cpu/proc.c               |  7 +++--
>   drivers/cpufreq/Kconfig.x86              | 12 ++++++++
>   drivers/cpufreq/cpufreq.c                | 36 +++++++++++++++++++++---
>   include/linux/cpufreq.h                  |  2 +-
>   6 files changed, 66 insertions(+), 9 deletions(-)
> 
> diff --git a/Documentation/admin-guide/pm/cpufreq.rst b/Documentation/admin-guide/pm/cpufreq.rst
> index fe1be4ad88cb..76f3835afe01 100644
> --- a/Documentation/admin-guide/pm/cpufreq.rst
> +++ b/Documentation/admin-guide/pm/cpufreq.rst
> @@ -248,6 +248,19 @@ are the following:
>   	If that frequency cannot be determined, this attribute should not
>   	be present.
>   
> +``cpuinfo_avg_freq``
> +        An average frequency (in KHz) of all CPUs belonging to a given policy,
> +        derived from a hardware provided feedback and reported on a time frame
> +        spanning at most few milliseconds.
> +
> +        This is expected to be based on the frequency the hardware actually runs
> +        at and, as such, might require specialised hardware support (such as AMU
> +        extension on ARM). If one cannot be determined, this attribute should
> +        not be present.
> +
> +        Note, that failed attempt to retrieve current frequency for a given
> +        CPU(s) will result in an appropriate error.
> +
>   ``cpuinfo_max_freq``
>   	Maximum possible operating frequency the CPUs belonging to this policy
>   	can run at (in kHz).
> @@ -293,7 +306,8 @@ are the following:
>   	Some architectures (e.g. ``x86``) may attempt to provide information
>   	more precisely reflecting the current CPU frequency through this
>   	attribute, but that still may not be the exact current CPU frequency as
> -	seen by the hardware at the moment.
> +	seen by the hardware at the moment. This behavior though, is only
> +	available via c:macro:``CPUFREQ_ARCH_CUR_FREQ`` option.
>   
>   ``scaling_driver``
>   	The scaling driver currently in use.
> diff --git a/arch/x86/kernel/cpu/aperfmperf.c b/arch/x86/kernel/cpu/aperfmperf.c
> index 0b69bfbf345d..a00059139ca4 100644
> --- a/arch/x86/kernel/cpu/aperfmperf.c
> +++ b/arch/x86/kernel/cpu/aperfmperf.c
> @@ -413,7 +413,7 @@ void arch_scale_freq_tick(void)
>    */
>   #define MAX_SAMPLE_AGE	((unsigned long)HZ / 50)
>   
> -unsigned int arch_freq_get_on_cpu(int cpu)
> +int arch_freq_get_on_cpu(int cpu)
>   {
>   	struct aperfmperf *s = per_cpu_ptr(&cpu_samples, cpu);
>   	unsigned int seq, freq;
> diff --git a/arch/x86/kernel/cpu/proc.c b/arch/x86/kernel/cpu/proc.c
> index e65fae63660e..34d8fb93fb70 100644
> --- a/arch/x86/kernel/cpu/proc.c
> +++ b/arch/x86/kernel/cpu/proc.c
> @@ -86,9 +86,12 @@ static int show_cpuinfo(struct seq_file *m, void *v)
>   		seq_printf(m, "microcode\t: 0x%x\n", c->microcode);
>   
>   	if (cpu_has(c, X86_FEATURE_TSC)) {
> -		unsigned int freq = arch_freq_get_on_cpu(cpu);
> +		int freq = arch_freq_get_on_cpu(cpu);
>   
> -		seq_printf(m, "cpu MHz\t\t: %u.%03u\n", freq / 1000, (freq % 1000));
> +		if (freq <= 0)
> +			seq_puts(m, "cpu MHz\t\t: Unknown\n");
> +		else
> +			seq_printf(m, "cpu MHz\t\t: %u.%03u\n", freq / 1000, (freq % 1000));
>   	}
>   
>   	/* Cache size */
> diff --git a/drivers/cpufreq/Kconfig.x86 b/drivers/cpufreq/Kconfig.x86
> index 97c2d4f15d76..212e1b9afe21 100644
> --- a/drivers/cpufreq/Kconfig.x86
> +++ b/drivers/cpufreq/Kconfig.x86
> @@ -340,3 +340,15 @@ config X86_SPEEDSTEP_RELAXED_CAP_CHECK
>   	  option lets the probing code bypass some of those checks if the
>   	  parameter "relaxed_check=1" is passed to the module.
>   
> +config CPUFREQ_ARCH_CUR_FREQ
> +	default y
> +	bool "Current frequency derived from HW provided feedback"
> +	help
> +	  This determines whether the scaling_cur_freq sysfs attribute returns
> +	  the last requested frequency or a more precise value based on hardware
> +	  provided feedback (as architected counters).
> +	  Given that a more precise frequency can now be provided via the
> +	  cpuinfo_avg_cur_freq attribute, by enabling this option,
> +	  scaling_cur_freq maintains the provision of a counter based frequency,
> +	  for compatibility reasons.
> +
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 04fc786dd2c0..70df2a24437b 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -747,9 +747,14 @@ show_one(cpuinfo_transition_latency, cpuinfo.transition_latency);
>   show_one(scaling_min_freq, min);
>   show_one(scaling_max_freq, max);
>   
> -__weak unsigned int arch_freq_get_on_cpu(int cpu)
> +__weak int arch_freq_get_on_cpu(int cpu)
>   {
> -	return 0;
> +	return -EOPNOTSUPP;
> +}
> +
> +static inline bool cpufreq_avg_freq_supported(struct cpufreq_policy *policy)
> +{
> +	return arch_freq_get_on_cpu(policy->cpu) != -EOPNOTSUPP;
>   }
>   
>   static ssize_t show_scaling_cur_freq(struct cpufreq_policy *policy, char *buf)
> @@ -757,8 +762,11 @@ static ssize_t show_scaling_cur_freq(struct cpufreq_policy *policy, char *buf)
>   	ssize_t ret;
>   	unsigned int freq;
>   
> -	freq = arch_freq_get_on_cpu(policy->cpu);
> -	if (freq)
> +	freq = IS_ENABLED(CONFIG_CPUFREQ_ARCH_CUR_FREQ)
> +		? arch_freq_get_on_cpu(policy->cpu)
> +		: 0;
> +
> +	if (freq > 0)
>   		ret = sysfs_emit(buf, "%u\n", freq);
>   	else if (cpufreq_driver->setpolicy && cpufreq_driver->get)
>   		ret = sysfs_emit(buf, "%u\n", cpufreq_driver->get(policy->cpu));
> @@ -802,6 +810,19 @@ static ssize_t show_cpuinfo_cur_freq(struct cpufreq_policy *policy,
>   	return sysfs_emit(buf, "<unknown>\n");
>   }
>   
> +/*
> + * show_cpuinfo_avg_freq - average CPU frequency as detected by hardware
> + */
> +static ssize_t show_cpuinfo_avg_freq(struct cpufreq_policy *policy,
> +				     char *buf)
> +{
> +	int avg_freq = arch_freq_get_on_cpu(policy->cpu);

We are seeing issues when reading cpuinfo_avg_freq on an ARM64 system:

$ cat /sys/devices/system/cpu/cpufreq/policy1/cpuinfo_avg_freq
cat: /sys/devices/system/cpu/cpufreq/policy1/cpuinfo_avg_freq: Resource 
temporarily unavailable

The CPU is in idle state, so arch_freq_get_on_cpu() can't find a good 
alternative source for frequency info.

One way to resolve this is to have fallback methods in show_cpuinfo_avg_freq() 
so it will look like this:

static ssize_t show_cpuinfo_avg_freq(struct cpufreq_policy *policy,
                                      char *buf)
{
         int avg_freq = arch_freq_get_on_cpu(policy->cpu);
         int ret;

         if (avg_freq > 0)
                 ret = sysfs_emit(buf, "%u\n", avg_freq);
         else if (cpufreq_driver->setpolicy && cpufreq_driver->get)
                 ret = sysfs_emit(buf, "%u\n", cpufreq_driver->get(policy->cpu));
         else
                 ret = sysfs_emit(buf, "%u\n", policy->cur);
         return ret;
}

But that also makes show_cpuinfo_avg_freq() pretty much the same as 
show_scaling_cur_freq().

So is it possible to consolidate show_cpuinfo_avg_freq() into 
show_scaling_cur_freq(), by making CONFIG_CPUFREQ_ARCH_CUR_FREQ also available 
to ARM64?

Kai-Heng

> +
> +	if (avg_freq > 0)
> +		return sysfs_emit(buf, "%u\n", avg_freq);
> +	return avg_freq != 0 ? avg_freq : -EINVAL;
> +}
> +
>   /*
>    * show_scaling_governor - show the current policy for the specified CPU
>    */
> @@ -964,6 +985,7 @@ static ssize_t show_bios_limit(struct cpufreq_policy *policy, char *buf)
>   }
>   
>   cpufreq_freq_attr_ro_perm(cpuinfo_cur_freq, 0400);
> +cpufreq_freq_attr_ro(cpuinfo_avg_freq);
>   cpufreq_freq_attr_ro(cpuinfo_min_freq);
>   cpufreq_freq_attr_ro(cpuinfo_max_freq);
>   cpufreq_freq_attr_ro(cpuinfo_transition_latency);
> @@ -1091,6 +1113,12 @@ static int cpufreq_add_dev_interface(struct cpufreq_policy *policy)
>   			return ret;
>   	}
>   
> +	if (cpufreq_avg_freq_supported(policy)) {
> +		ret = sysfs_create_file(&policy->kobj, &cpuinfo_avg_freq.attr);
> +		if (ret)
> +			return ret;
> +	}
> +
>   	ret = sysfs_create_file(&policy->kobj, &scaling_cur_freq.attr);
>   	if (ret)
>   		return ret;
> diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
> index d4d2f4d1d7cb..a7b6c0ccf9bc 100644
> --- a/include/linux/cpufreq.h
> +++ b/include/linux/cpufreq.h
> @@ -1194,7 +1194,7 @@ static inline int of_perf_domain_get_sharing_cpumask(int pcpu, const char *list_
>   }
>   #endif
>   
> -extern unsigned int arch_freq_get_on_cpu(int cpu);
> +extern int arch_freq_get_on_cpu(int cpu);
>   
>   #ifndef arch_set_freq_scale
>   static __always_inline

Re: [PATCH v8 1/4] cpufreq: Introduce an optional cpuinfo_avg_freq sysfs entry

[Sumit Gupta]

On 16/12/24 11:13, Kai-Heng Feng wrote:
> Hi Beata,
> 
> On 2024/12/6 9:55 PM, Beata Michalska wrote:
>> Currently the CPUFreq core exposes two sysfs attributes that can be used
>> to query current frequency of a given CPU(s): namely cpuinfo_cur_freq
>> and scaling_cur_freq. Both provide slightly different view on the
>> subject and they do come with their own drawbacks.
>>
>> cpuinfo_cur_freq provides higher precision though at a cost of being
>> rather expensive. Moreover, the information retrieved via this attribute
>> is somewhat short lived as frequency can change at any point of time
>> making it difficult to reason from.
>>
>> scaling_cur_freq, on the other hand, tends to be less accurate but then
>> the actual level of precision (and source of information) varies between
>> architectures making it a bit ambiguous.
>>
>> The new attribute, cpuinfo_avg_freq, is intended to provide more stable,
>> distinct interface, exposing an average frequency of a given CPU(s), as
>> reported by the hardware, over a time frame spanning no more than a few
>> milliseconds. As it requires appropriate hardware support, this
>> interface is optional.
>>
>> Note that under the hood, the new attribute relies on the information
>> provided by arch_freq_get_on_cpu, which, up to this point, has been
>> feeding data for scaling_cur_freq attribute, being the source of
>> ambiguity when it comes to interpretation. This has been amended by
>> restoring the intended behavior for scaling_cur_freq, with a new
>> dedicated config option to maintain status quo for those, who may need
>> it.
>>
>> CC: Jonathan Corbet <corbet@lwn.net>
>> CC: Thomas Gleixner <tglx@linutronix.de>
>> CC: Ingo Molnar <mingo@redhat.com>
>> CC: Borislav Petkov <bp@alien8.de>
>> CC: Dave Hansen <dave.hansen@linux.intel.com>
>> CC: H. Peter Anvin <hpa@zytor.com>
>> CC: Phil Auld <pauld@redhat.com>
>> CC: x86@kernel.org
>> CC: linux-doc@vger.kernel.org
>> Signed-off-by: Beata Michalska <beata.michalska@arm.com>
>> ---
>>   Documentation/admin-guide/pm/cpufreq.rst | 16 ++++++++++-
>>   arch/x86/kernel/cpu/aperfmperf.c         |  2 +-
>>   arch/x86/kernel/cpu/proc.c               |  7 +++--
>>   drivers/cpufreq/Kconfig.x86              | 12 ++++++++
>>   drivers/cpufreq/cpufreq.c                | 36 +++++++++++++++++++++---
>>   include/linux/cpufreq.h                  |  2 +-
>>   6 files changed, 66 insertions(+), 9 deletions(-)
>>
>> diff --git a/Documentation/admin-guide/pm/cpufreq.rst 
>> b/Documentation/admin-guide/pm/cpufreq.rst
>> index fe1be4ad88cb..76f3835afe01 100644
>> --- a/Documentation/admin-guide/pm/cpufreq.rst
>> +++ b/Documentation/admin-guide/pm/cpufreq.rst
>> @@ -248,6 +248,19 @@ are the following:
>>       If that frequency cannot be determined, this attribute should not
>>       be present.
>> +``cpuinfo_avg_freq``
>> +        An average frequency (in KHz) of all CPUs belonging to a 
>> given policy,
>> +        derived from a hardware provided feedback and reported on a 
>> time frame
>> +        spanning at most few milliseconds.
>> +
>> +        This is expected to be based on the frequency the hardware 
>> actually runs
>> +        at and, as such, might require specialised hardware support 
>> (such as AMU
>> +        extension on ARM). If one cannot be determined, this 
>> attribute should
>> +        not be present.
>> +
>> +        Note, that failed attempt to retrieve current frequency for a 
>> given
>> +        CPU(s) will result in an appropriate error.
>> +
>>   ``cpuinfo_max_freq``
>>       Maximum possible operating frequency the CPUs belonging to this 
>> policy
>>       can run at (in kHz).
>> @@ -293,7 +306,8 @@ are the following:
>>       Some architectures (e.g. ``x86``) may attempt to provide 
>> information
>>       more precisely reflecting the current CPU frequency through this
>>       attribute, but that still may not be the exact current CPU 
>> frequency as
>> -    seen by the hardware at the moment.
>> +    seen by the hardware at the moment. This behavior though, is only
>> +    available via c:macro:``CPUFREQ_ARCH_CUR_FREQ`` option.
>>   ``scaling_driver``
>>       The scaling driver currently in use.
>> diff --git a/arch/x86/kernel/cpu/aperfmperf.c 
>> b/arch/x86/kernel/cpu/aperfmperf.c
>> index 0b69bfbf345d..a00059139ca4 100644
>> --- a/arch/x86/kernel/cpu/aperfmperf.c
>> +++ b/arch/x86/kernel/cpu/aperfmperf.c
>> @@ -413,7 +413,7 @@ void arch_scale_freq_tick(void)
>>    */
>>   #define MAX_SAMPLE_AGE    ((unsigned long)HZ / 50)
>> -unsigned int arch_freq_get_on_cpu(int cpu)
>> +int arch_freq_get_on_cpu(int cpu)
>>   {
>>       struct aperfmperf *s = per_cpu_ptr(&cpu_samples, cpu);
>>       unsigned int seq, freq;
>> diff --git a/arch/x86/kernel/cpu/proc.c b/arch/x86/kernel/cpu/proc.c
>> index e65fae63660e..34d8fb93fb70 100644
>> --- a/arch/x86/kernel/cpu/proc.c
>> +++ b/arch/x86/kernel/cpu/proc.c
>> @@ -86,9 +86,12 @@ static int show_cpuinfo(struct seq_file *m, void *v)
>>           seq_printf(m, "microcode\t: 0x%x\n", c->microcode);
>>       if (cpu_has(c, X86_FEATURE_TSC)) {
>> -        unsigned int freq = arch_freq_get_on_cpu(cpu);
>> +        int freq = arch_freq_get_on_cpu(cpu);
>> -        seq_printf(m, "cpu MHz\t\t: %u.%03u\n", freq / 1000, (freq % 
>> 1000));
>> +        if (freq <= 0)
>> +            seq_puts(m, "cpu MHz\t\t: Unknown\n");
>> +        else
>> +            seq_printf(m, "cpu MHz\t\t: %u.%03u\n", freq / 1000, 
>> (freq % 1000));
>>       }
>>       /* Cache size */
>> diff --git a/drivers/cpufreq/Kconfig.x86 b/drivers/cpufreq/Kconfig.x86
>> index 97c2d4f15d76..212e1b9afe21 100644
>> --- a/drivers/cpufreq/Kconfig.x86
>> +++ b/drivers/cpufreq/Kconfig.x86
>> @@ -340,3 +340,15 @@ config X86_SPEEDSTEP_RELAXED_CAP_CHECK
>>         option lets the probing code bypass some of those checks if the
>>         parameter "relaxed_check=1" is passed to the module.
>> +config CPUFREQ_ARCH_CUR_FREQ
>> +    default y
>> +    bool "Current frequency derived from HW provided feedback"
>> +    help
>> +      This determines whether the scaling_cur_freq sysfs attribute 
>> returns
>> +      the last requested frequency or a more precise value based on 
>> hardware
>> +      provided feedback (as architected counters).
>> +      Given that a more precise frequency can now be provided via the
>> +      cpuinfo_avg_cur_freq attribute, by enabling this option,
>> +      scaling_cur_freq maintains the provision of a counter based 
>> frequency,
>> +      for compatibility reasons.
>> +
>> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
>> index 04fc786dd2c0..70df2a24437b 100644
>> --- a/drivers/cpufreq/cpufreq.c
>> +++ b/drivers/cpufreq/cpufreq.c
>> @@ -747,9 +747,14 @@ show_one(cpuinfo_transition_latency, 
>> cpuinfo.transition_latency);
>>   show_one(scaling_min_freq, min);
>>   show_one(scaling_max_freq, max);
>> -__weak unsigned int arch_freq_get_on_cpu(int cpu)
>> +__weak int arch_freq_get_on_cpu(int cpu)
>>   {
>> -    return 0;
>> +    return -EOPNOTSUPP;
>> +}
>> +
>> +static inline bool cpufreq_avg_freq_supported(struct cpufreq_policy 
>> *policy)
>> +{
>> +    return arch_freq_get_on_cpu(policy->cpu) != -EOPNOTSUPP;
>>   }
>>   static ssize_t show_scaling_cur_freq(struct cpufreq_policy *policy, 
>> char *buf)
>> @@ -757,8 +762,11 @@ static ssize_t show_scaling_cur_freq(struct 
>> cpufreq_policy *policy, char *buf)
>>       ssize_t ret;
>>       unsigned int freq;
>> -    freq = arch_freq_get_on_cpu(policy->cpu);
>> -    if (freq)
>> +    freq = IS_ENABLED(CONFIG_CPUFREQ_ARCH_CUR_FREQ)
>> +        ? arch_freq_get_on_cpu(policy->cpu)
>> +        : 0;
>> +
>> +    if (freq > 0)
>>           ret = sysfs_emit(buf, "%u\n", freq);
>>       else if (cpufreq_driver->setpolicy && cpufreq_driver->get)
>>           ret = sysfs_emit(buf, "%u\n", 
>> cpufreq_driver->get(policy->cpu));
>> @@ -802,6 +810,19 @@ static ssize_t show_cpuinfo_cur_freq(struct 
>> cpufreq_policy *policy,
>>       return sysfs_emit(buf, "<unknown>\n");
>>   }
>> +/*
>> + * show_cpuinfo_avg_freq - average CPU frequency as detected by hardware
>> + */
>> +static ssize_t show_cpuinfo_avg_freq(struct cpufreq_policy *policy,
>> +                     char *buf)
>> +{
>> +    int avg_freq = arch_freq_get_on_cpu(policy->cpu);
> 
> We are seeing issues when reading cpuinfo_avg_freq on an ARM64 system:
> 
> $ cat /sys/devices/system/cpu/cpufreq/policy1/cpuinfo_avg_freq
> cat: /sys/devices/system/cpu/cpufreq/policy1/cpuinfo_avg_freq: Resource 
> temporarily unavailable
> 
> The CPU is in idle state, so arch_freq_get_on_cpu() can't find a good 
> alternative source for frequency info.
> 

Hi Kai Heng,
This has already been discussed during v7 in [1] & [2].
In v7, we were returning zero which printed 'unknown'.
The discussion was about printing in more descriptive way or with an 
appropriate error code. In v8 we are returning 'EAGAIN' instead of zero. 
The final decision was of Maintainers.

Viresh,
You have any preference on this?

[1] 
https://lore.kernel.org/lkml/aa254516-968e-4665-bb5b-981c296ffc35@nvidia.com/#t
[2] https://lore.kernel.org/lkml/Zyh-uVSW-0d0r8oB@arm.com/

Thank you,
Sumit Gupta

> One way to resolve this is to have fallback methods in 
> show_cpuinfo_avg_freq() so it will look like this:
> 
> static ssize_t show_cpuinfo_avg_freq(struct cpufreq_policy *policy,
>                                       char *buf)
> {
>          int avg_freq = arch_freq_get_on_cpu(policy->cpu);
>          int ret;
> 
>          if (avg_freq > 0)
>                  ret = sysfs_emit(buf, "%u\n", avg_freq);
>          else if (cpufreq_driver->setpolicy && cpufreq_driver->get)
>                  ret = sysfs_emit(buf, "%u\n", 
> cpufreq_driver->get(policy->cpu));
>          else
>                  ret = sysfs_emit(buf, "%u\n", policy->cur);
>          return ret;
> }
> 
> But that also makes show_cpuinfo_avg_freq() pretty much the same as 
> show_scaling_cur_freq().
> 
> So is it possible to consolidate show_cpuinfo_avg_freq() into 
> show_scaling_cur_freq(), by making CONFIG_CPUFREQ_ARCH_CUR_FREQ also 
> available to ARM64?
> 
> Kai-Heng
> 
>> +
>> +    if (avg_freq > 0)
>> +        return sysfs_emit(buf, "%u\n", avg_freq);
>> +    return avg_freq != 0 ? avg_freq : -EINVAL;
>> +}
>> +
>>   /*
>>    * show_scaling_governor - show the current policy for the specified 
>> CPU
>>    */
>> @@ -964,6 +985,7 @@ static ssize_t show_bios_limit(struct 
>> cpufreq_policy *policy, char *buf)
>>   }
>>   cpufreq_freq_attr_ro_perm(cpuinfo_cur_freq, 0400);
>> +cpufreq_freq_attr_ro(cpuinfo_avg_freq);
>>   cpufreq_freq_attr_ro(cpuinfo_min_freq);
>>   cpufreq_freq_attr_ro(cpuinfo_max_freq);
>>   cpufreq_freq_attr_ro(cpuinfo_transition_latency);
>> @@ -1091,6 +1113,12 @@ static int cpufreq_add_dev_interface(struct 
>> cpufreq_policy *policy)
>>               return ret;
>>       }
>> +    if (cpufreq_avg_freq_supported(policy)) {
>> +        ret = sysfs_create_file(&policy->kobj, &cpuinfo_avg_freq.attr);
>> +        if (ret)
>> +            return ret;
>> +    }
>> +
>>       ret = sysfs_create_file(&policy->kobj, &scaling_cur_freq.attr);
>>       if (ret)
>>           return ret;
>> diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
>> index d4d2f4d1d7cb..a7b6c0ccf9bc 100644
>> --- a/include/linux/cpufreq.h
>> +++ b/include/linux/cpufreq.h
>> @@ -1194,7 +1194,7 @@ static inline int 
>> of_perf_domain_get_sharing_cpumask(int pcpu, const char *list_
>>   }
>>   #endif
>> -extern unsigned int arch_freq_get_on_cpu(int cpu);
>> +extern int arch_freq_get_on_cpu(int cpu);
>>   #ifndef arch_set_freq_scale
>>   static __always_inline
> 

Re: [PATCH v8 1/4] cpufreq: Introduce an optional cpuinfo_avg_freq sysfs entry

[Kai-Heng Feng]

Hi Sumit,

On 2024/12/16 3:11 PM, Sumit Gupta wrote:
> 
> 
> On 16/12/24 11:13, Kai-Heng Feng wrote:
>> Hi Beata,
>>
>> On 2024/12/6 9:55 PM, Beata Michalska wrote:
>>> Currently the CPUFreq core exposes two sysfs attributes that can be used
>>> to query current frequency of a given CPU(s): namely cpuinfo_cur_freq
>>> and scaling_cur_freq. Both provide slightly different view on the
>>> subject and they do come with their own drawbacks.
>>>
>>> cpuinfo_cur_freq provides higher precision though at a cost of being
>>> rather expensive. Moreover, the information retrieved via this attribute
>>> is somewhat short lived as frequency can change at any point of time
>>> making it difficult to reason from.
>>>
>>> scaling_cur_freq, on the other hand, tends to be less accurate but then
>>> the actual level of precision (and source of information) varies between
>>> architectures making it a bit ambiguous.
>>>
>>> The new attribute, cpuinfo_avg_freq, is intended to provide more stable,
>>> distinct interface, exposing an average frequency of a given CPU(s), as
>>> reported by the hardware, over a time frame spanning no more than a few
>>> milliseconds. As it requires appropriate hardware support, this
>>> interface is optional.
>>>
>>> Note that under the hood, the new attribute relies on the information
>>> provided by arch_freq_get_on_cpu, which, up to this point, has been
>>> feeding data for scaling_cur_freq attribute, being the source of
>>> ambiguity when it comes to interpretation. This has been amended by
>>> restoring the intended behavior for scaling_cur_freq, with a new
>>> dedicated config option to maintain status quo for those, who may need
>>> it.
>>>
>>> CC: Jonathan Corbet <corbet@lwn.net>
>>> CC: Thomas Gleixner <tglx@linutronix.de>
>>> CC: Ingo Molnar <mingo@redhat.com>
>>> CC: Borislav Petkov <bp@alien8.de>
>>> CC: Dave Hansen <dave.hansen@linux.intel.com>
>>> CC: H. Peter Anvin <hpa@zytor.com>
>>> CC: Phil Auld <pauld@redhat.com>
>>> CC: x86@kernel.org
>>> CC: linux-doc@vger.kernel.org
>>> Signed-off-by: Beata Michalska <beata.michalska@arm.com>
>>> ---
>>>   Documentation/admin-guide/pm/cpufreq.rst | 16 ++++++++++-
>>>   arch/x86/kernel/cpu/aperfmperf.c         |  2 +-
>>>   arch/x86/kernel/cpu/proc.c               |  7 +++--
>>>   drivers/cpufreq/Kconfig.x86              | 12 ++++++++
>>>   drivers/cpufreq/cpufreq.c                | 36 +++++++++++++++++++++---
>>>   include/linux/cpufreq.h                  |  2 +-
>>>   6 files changed, 66 insertions(+), 9 deletions(-)
>>>
>>> diff --git a/Documentation/admin-guide/pm/cpufreq.rst b/Documentation/admin- 
>>> guide/pm/cpufreq.rst
>>> index fe1be4ad88cb..76f3835afe01 100644
>>> --- a/Documentation/admin-guide/pm/cpufreq.rst
>>> +++ b/Documentation/admin-guide/pm/cpufreq.rst
>>> @@ -248,6 +248,19 @@ are the following:
>>>       If that frequency cannot be determined, this attribute should not
>>>       be present.
>>> +``cpuinfo_avg_freq``
>>> +        An average frequency (in KHz) of all CPUs belonging to a given policy,
>>> +        derived from a hardware provided feedback and reported on a time frame
>>> +        spanning at most few milliseconds.
>>> +
>>> +        This is expected to be based on the frequency the hardware actually 
>>> runs
>>> +        at and, as such, might require specialised hardware support (such as 
>>> AMU
>>> +        extension on ARM). If one cannot be determined, this attribute should
>>> +        not be present.
>>> +
>>> +        Note, that failed attempt to retrieve current frequency for a given
>>> +        CPU(s) will result in an appropriate error.
>>> +
>>>   ``cpuinfo_max_freq``
>>>       Maximum possible operating frequency the CPUs belonging to this policy
>>>       can run at (in kHz).
>>> @@ -293,7 +306,8 @@ are the following:
>>>       Some architectures (e.g. ``x86``) may attempt to provide information
>>>       more precisely reflecting the current CPU frequency through this
>>>       attribute, but that still may not be the exact current CPU frequency as
>>> -    seen by the hardware at the moment.
>>> +    seen by the hardware at the moment. This behavior though, is only
>>> +    available via c:macro:``CPUFREQ_ARCH_CUR_FREQ`` option.
>>>   ``scaling_driver``
>>>       The scaling driver currently in use.
>>> diff --git a/arch/x86/kernel/cpu/aperfmperf.c b/arch/x86/kernel/cpu/aperfmperf.c
>>> index 0b69bfbf345d..a00059139ca4 100644
>>> --- a/arch/x86/kernel/cpu/aperfmperf.c
>>> +++ b/arch/x86/kernel/cpu/aperfmperf.c
>>> @@ -413,7 +413,7 @@ void arch_scale_freq_tick(void)
>>>    */
>>>   #define MAX_SAMPLE_AGE    ((unsigned long)HZ / 50)
>>> -unsigned int arch_freq_get_on_cpu(int cpu)
>>> +int arch_freq_get_on_cpu(int cpu)
>>>   {
>>>       struct aperfmperf *s = per_cpu_ptr(&cpu_samples, cpu);
>>>       unsigned int seq, freq;
>>> diff --git a/arch/x86/kernel/cpu/proc.c b/arch/x86/kernel/cpu/proc.c
>>> index e65fae63660e..34d8fb93fb70 100644
>>> --- a/arch/x86/kernel/cpu/proc.c
>>> +++ b/arch/x86/kernel/cpu/proc.c
>>> @@ -86,9 +86,12 @@ static int show_cpuinfo(struct seq_file *m, void *v)
>>>           seq_printf(m, "microcode\t: 0x%x\n", c->microcode);
>>>       if (cpu_has(c, X86_FEATURE_TSC)) {
>>> -        unsigned int freq = arch_freq_get_on_cpu(cpu);
>>> +        int freq = arch_freq_get_on_cpu(cpu);
>>> -        seq_printf(m, "cpu MHz\t\t: %u.%03u\n", freq / 1000, (freq % 1000));
>>> +        if (freq <= 0)
>>> +            seq_puts(m, "cpu MHz\t\t: Unknown\n");
>>> +        else
>>> +            seq_printf(m, "cpu MHz\t\t: %u.%03u\n", freq / 1000, (freq % 
>>> 1000));
>>>       }
>>>       /* Cache size */
>>> diff --git a/drivers/cpufreq/Kconfig.x86 b/drivers/cpufreq/Kconfig.x86
>>> index 97c2d4f15d76..212e1b9afe21 100644
>>> --- a/drivers/cpufreq/Kconfig.x86
>>> +++ b/drivers/cpufreq/Kconfig.x86
>>> @@ -340,3 +340,15 @@ config X86_SPEEDSTEP_RELAXED_CAP_CHECK
>>>         option lets the probing code bypass some of those checks if the
>>>         parameter "relaxed_check=1" is passed to the module.
>>> +config CPUFREQ_ARCH_CUR_FREQ
>>> +    default y
>>> +    bool "Current frequency derived from HW provided feedback"
>>> +    help
>>> +      This determines whether the scaling_cur_freq sysfs attribute returns
>>> +      the last requested frequency or a more precise value based on hardware
>>> +      provided feedback (as architected counters).
>>> +      Given that a more precise frequency can now be provided via the
>>> +      cpuinfo_avg_cur_freq attribute, by enabling this option,
>>> +      scaling_cur_freq maintains the provision of a counter based frequency,
>>> +      for compatibility reasons.
>>> +
>>> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
>>> index 04fc786dd2c0..70df2a24437b 100644
>>> --- a/drivers/cpufreq/cpufreq.c
>>> +++ b/drivers/cpufreq/cpufreq.c
>>> @@ -747,9 +747,14 @@ show_one(cpuinfo_transition_latency, 
>>> cpuinfo.transition_latency);
>>>   show_one(scaling_min_freq, min);
>>>   show_one(scaling_max_freq, max);
>>> -__weak unsigned int arch_freq_get_on_cpu(int cpu)
>>> +__weak int arch_freq_get_on_cpu(int cpu)
>>>   {
>>> -    return 0;
>>> +    return -EOPNOTSUPP;
>>> +}
>>> +
>>> +static inline bool cpufreq_avg_freq_supported(struct cpufreq_policy *policy)
>>> +{
>>> +    return arch_freq_get_on_cpu(policy->cpu) != -EOPNOTSUPP;
>>>   }
>>>   static ssize_t show_scaling_cur_freq(struct cpufreq_policy *policy, char *buf)
>>> @@ -757,8 +762,11 @@ static ssize_t show_scaling_cur_freq(struct 
>>> cpufreq_policy *policy, char *buf)
>>>       ssize_t ret;
>>>       unsigned int freq;
>>> -    freq = arch_freq_get_on_cpu(policy->cpu);
>>> -    if (freq)
>>> +    freq = IS_ENABLED(CONFIG_CPUFREQ_ARCH_CUR_FREQ)
>>> +        ? arch_freq_get_on_cpu(policy->cpu)
>>> +        : 0;
>>> +
>>> +    if (freq > 0)
>>>           ret = sysfs_emit(buf, "%u\n", freq);
>>>       else if (cpufreq_driver->setpolicy && cpufreq_driver->get)
>>>           ret = sysfs_emit(buf, "%u\n", cpufreq_driver->get(policy->cpu));
>>> @@ -802,6 +810,19 @@ static ssize_t show_cpuinfo_cur_freq(struct 
>>> cpufreq_policy *policy,
>>>       return sysfs_emit(buf, "<unknown>\n");
>>>   }
>>> +/*
>>> + * show_cpuinfo_avg_freq - average CPU frequency as detected by hardware
>>> + */
>>> +static ssize_t show_cpuinfo_avg_freq(struct cpufreq_policy *policy,
>>> +                     char *buf)
>>> +{
>>> +    int avg_freq = arch_freq_get_on_cpu(policy->cpu);
>>
>> We are seeing issues when reading cpuinfo_avg_freq on an ARM64 system:
>>
>> $ cat /sys/devices/system/cpu/cpufreq/policy1/cpuinfo_avg_freq
>> cat: /sys/devices/system/cpu/cpufreq/policy1/cpuinfo_avg_freq: Resource 
>> temporarily unavailable
>>
>> The CPU is in idle state, so arch_freq_get_on_cpu() can't find a good 
>> alternative source for frequency info.
>>
> 
> Hi Kai Heng,
> This has already been discussed during v7 in [1] & [2].

Thanks for the info!

> In v7, we were returning zero which printed 'unknown'.
> The discussion was about printing in more descriptive way or with an appropriate 
> error code. In v8 we are returning 'EAGAIN' instead of zero. The final decision 
> was of Maintainers.

Is there any cpufreq driver that prints "unknown" or error when CPU is in idle?

I think it's more unsurprising to print the lowest CPU frequency when CPU is in 
idle state, instead of any other error code.

Kai-Heng

> 
> Viresh,
> You have any preference on this?
> 
> [1] https://lore.kernel.org/lkml/aa254516-968e-4665-bb5b-981c296ffc35@nvidia.com/#t
> [2] https://lore.kernel.org/lkml/Zyh-uVSW-0d0r8oB@arm.com/
> 
> Thank you,
> Sumit Gupta
> 
>> One way to resolve this is to have fallback methods in show_cpuinfo_avg_freq() 
>> so it will look like this:
>>
>> static ssize_t show_cpuinfo_avg_freq(struct cpufreq_policy *policy,
>>                                       char *buf)
>> {
>>          int avg_freq = arch_freq_get_on_cpu(policy->cpu);
>>          int ret;
>>
>>          if (avg_freq > 0)
>>                  ret = sysfs_emit(buf, "%u\n", avg_freq);
>>          else if (cpufreq_driver->setpolicy && cpufreq_driver->get)
>>                  ret = sysfs_emit(buf, "%u\n", cpufreq_driver->get(policy->cpu));
>>          else
>>                  ret = sysfs_emit(buf, "%u\n", policy->cur);
>>          return ret;
>> }
>>
>> But that also makes show_cpuinfo_avg_freq() pretty much the same as 
>> show_scaling_cur_freq().
>>
>> So is it possible to consolidate show_cpuinfo_avg_freq() into 
>> show_scaling_cur_freq(), by making CONFIG_CPUFREQ_ARCH_CUR_FREQ also available 
>> to ARM64?
>>
>> Kai-Heng
>>
>>> +
>>> +    if (avg_freq > 0)
>>> +        return sysfs_emit(buf, "%u\n", avg_freq);
>>> +    return avg_freq != 0 ? avg_freq : -EINVAL;
>>> +}
>>> +
>>>   /*
>>>    * show_scaling_governor - show the current policy for the specified CPU
>>>    */
>>> @@ -964,6 +985,7 @@ static ssize_t show_bios_limit(struct cpufreq_policy 
>>> *policy, char *buf)
>>>   }
>>>   cpufreq_freq_attr_ro_perm(cpuinfo_cur_freq, 0400);
>>> +cpufreq_freq_attr_ro(cpuinfo_avg_freq);
>>>   cpufreq_freq_attr_ro(cpuinfo_min_freq);
>>>   cpufreq_freq_attr_ro(cpuinfo_max_freq);
>>>   cpufreq_freq_attr_ro(cpuinfo_transition_latency);
>>> @@ -1091,6 +1113,12 @@ static int cpufreq_add_dev_interface(struct 
>>> cpufreq_policy *policy)
>>>               return ret;
>>>       }
>>> +    if (cpufreq_avg_freq_supported(policy)) {
>>> +        ret = sysfs_create_file(&policy->kobj, &cpuinfo_avg_freq.attr);
>>> +        if (ret)
>>> +            return ret;
>>> +    }
>>> +
>>>       ret = sysfs_create_file(&policy->kobj, &scaling_cur_freq.attr);
>>>       if (ret)
>>>           return ret;
>>> diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
>>> index d4d2f4d1d7cb..a7b6c0ccf9bc 100644
>>> --- a/include/linux/cpufreq.h
>>> +++ b/include/linux/cpufreq.h
>>> @@ -1194,7 +1194,7 @@ static inline int 
>>> of_perf_domain_get_sharing_cpumask(int pcpu, const char *list_
>>>   }
>>>   #endif
>>> -extern unsigned int arch_freq_get_on_cpu(int cpu);
>>> +extern int arch_freq_get_on_cpu(int cpu);
>>>   #ifndef arch_set_freq_scale
>>>   static __always_inline
>>

Re: [PATCH v8 1/4] cpufreq: Introduce an optional cpuinfo_avg_freq sysfs entry

[Beata Michalska]

On Mon, Dec 16, 2024 at 04:33:28PM +0800, Kai-Heng Feng wrote:
> Hi Sumit,
> 
> On 2024/12/16 3:11 PM, Sumit Gupta wrote:
> > 
> > 
> > On 16/12/24 11:13, Kai-Heng Feng wrote:
> > > Hi Beata,
> > > 
> > > On 2024/12/6 9:55 PM, Beata Michalska wrote:
> > > > Currently the CPUFreq core exposes two sysfs attributes that can be used
> > > > to query current frequency of a given CPU(s): namely cpuinfo_cur_freq
> > > > and scaling_cur_freq. Both provide slightly different view on the
> > > > subject and they do come with their own drawbacks.
> > > > 
> > > > cpuinfo_cur_freq provides higher precision though at a cost of being
> > > > rather expensive. Moreover, the information retrieved via this attribute
> > > > is somewhat short lived as frequency can change at any point of time
> > > > making it difficult to reason from.
> > > > 
> > > > scaling_cur_freq, on the other hand, tends to be less accurate but then
> > > > the actual level of precision (and source of information) varies between
> > > > architectures making it a bit ambiguous.
> > > > 
> > > > The new attribute, cpuinfo_avg_freq, is intended to provide more stable,
> > > > distinct interface, exposing an average frequency of a given CPU(s), as
> > > > reported by the hardware, over a time frame spanning no more than a few
> > > > milliseconds. As it requires appropriate hardware support, this
> > > > interface is optional.
> > > > 
> > > > Note that under the hood, the new attribute relies on the information
> > > > provided by arch_freq_get_on_cpu, which, up to this point, has been
> > > > feeding data for scaling_cur_freq attribute, being the source of
> > > > ambiguity when it comes to interpretation. This has been amended by
> > > > restoring the intended behavior for scaling_cur_freq, with a new
> > > > dedicated config option to maintain status quo for those, who may need
> > > > it.
> > > > 
> > > > CC: Jonathan Corbet <corbet@lwn.net>
> > > > CC: Thomas Gleixner <tglx@linutronix.de>
> > > > CC: Ingo Molnar <mingo@redhat.com>
> > > > CC: Borislav Petkov <bp@alien8.de>
> > > > CC: Dave Hansen <dave.hansen@linux.intel.com>
> > > > CC: H. Peter Anvin <hpa@zytor.com>
> > > > CC: Phil Auld <pauld@redhat.com>
> > > > CC: x86@kernel.org
> > > > CC: linux-doc@vger.kernel.org
> > > > Signed-off-by: Beata Michalska <beata.michalska@arm.com>
> > > > ---
> > > >   Documentation/admin-guide/pm/cpufreq.rst | 16 ++++++++++-
> > > >   arch/x86/kernel/cpu/aperfmperf.c         |  2 +-
> > > >   arch/x86/kernel/cpu/proc.c               |  7 +++--
> > > >   drivers/cpufreq/Kconfig.x86              | 12 ++++++++
> > > >   drivers/cpufreq/cpufreq.c                | 36 +++++++++++++++++++++---
> > > >   include/linux/cpufreq.h                  |  2 +-
> > > >   6 files changed, 66 insertions(+), 9 deletions(-)
> > > > 
> > > > diff --git a/Documentation/admin-guide/pm/cpufreq.rst
> > > > b/Documentation/admin- guide/pm/cpufreq.rst
> > > > index fe1be4ad88cb..76f3835afe01 100644
> > > > --- a/Documentation/admin-guide/pm/cpufreq.rst
> > > > +++ b/Documentation/admin-guide/pm/cpufreq.rst
> > > > @@ -248,6 +248,19 @@ are the following:
> > > >       If that frequency cannot be determined, this attribute should not
> > > >       be present.
> > > > +``cpuinfo_avg_freq``
> > > > +        An average frequency (in KHz) of all CPUs belonging to a given policy,
> > > > +        derived from a hardware provided feedback and reported on a time frame
> > > > +        spanning at most few milliseconds.
> > > > +
> > > > +        This is expected to be based on the frequency the
> > > > hardware actually runs
> > > > +        at and, as such, might require specialised hardware
> > > > support (such as AMU
> > > > +        extension on ARM). If one cannot be determined, this attribute should
> > > > +        not be present.
> > > > +
> > > > +        Note, that failed attempt to retrieve current frequency for a given
> > > > +        CPU(s) will result in an appropriate error.
> > > > +
> > > >   ``cpuinfo_max_freq``
> > > >       Maximum possible operating frequency the CPUs belonging to this policy
> > > >       can run at (in kHz).
> > > > @@ -293,7 +306,8 @@ are the following:
> > > >       Some architectures (e.g. ``x86``) may attempt to provide information
> > > >       more precisely reflecting the current CPU frequency through this
> > > >       attribute, but that still may not be the exact current CPU frequency as
> > > > -    seen by the hardware at the moment.
> > > > +    seen by the hardware at the moment. This behavior though, is only
> > > > +    available via c:macro:``CPUFREQ_ARCH_CUR_FREQ`` option.
> > > >   ``scaling_driver``
> > > >       The scaling driver currently in use.
> > > > diff --git a/arch/x86/kernel/cpu/aperfmperf.c b/arch/x86/kernel/cpu/aperfmperf.c
> > > > index 0b69bfbf345d..a00059139ca4 100644
> > > > --- a/arch/x86/kernel/cpu/aperfmperf.c
> > > > +++ b/arch/x86/kernel/cpu/aperfmperf.c
> > > > @@ -413,7 +413,7 @@ void arch_scale_freq_tick(void)
> > > >    */
> > > >   #define MAX_SAMPLE_AGE    ((unsigned long)HZ / 50)
> > > > -unsigned int arch_freq_get_on_cpu(int cpu)
> > > > +int arch_freq_get_on_cpu(int cpu)
> > > >   {
> > > >       struct aperfmperf *s = per_cpu_ptr(&cpu_samples, cpu);
> > > >       unsigned int seq, freq;
> > > > diff --git a/arch/x86/kernel/cpu/proc.c b/arch/x86/kernel/cpu/proc.c
> > > > index e65fae63660e..34d8fb93fb70 100644
> > > > --- a/arch/x86/kernel/cpu/proc.c
> > > > +++ b/arch/x86/kernel/cpu/proc.c
> > > > @@ -86,9 +86,12 @@ static int show_cpuinfo(struct seq_file *m, void *v)
> > > >           seq_printf(m, "microcode\t: 0x%x\n", c->microcode);
> > > >       if (cpu_has(c, X86_FEATURE_TSC)) {
> > > > -        unsigned int freq = arch_freq_get_on_cpu(cpu);
> > > > +        int freq = arch_freq_get_on_cpu(cpu);
> > > > -        seq_printf(m, "cpu MHz\t\t: %u.%03u\n", freq / 1000, (freq % 1000));
> > > > +        if (freq <= 0)
> > > > +            seq_puts(m, "cpu MHz\t\t: Unknown\n");
> > > > +        else
> > > > +            seq_printf(m, "cpu MHz\t\t: %u.%03u\n", freq /
> > > > 1000, (freq % 1000));
> > > >       }
> > > >       /* Cache size */
> > > > diff --git a/drivers/cpufreq/Kconfig.x86 b/drivers/cpufreq/Kconfig.x86
> > > > index 97c2d4f15d76..212e1b9afe21 100644
> > > > --- a/drivers/cpufreq/Kconfig.x86
> > > > +++ b/drivers/cpufreq/Kconfig.x86
> > > > @@ -340,3 +340,15 @@ config X86_SPEEDSTEP_RELAXED_CAP_CHECK
> > > >         option lets the probing code bypass some of those checks if the
> > > >         parameter "relaxed_check=1" is passed to the module.
> > > > +config CPUFREQ_ARCH_CUR_FREQ
> > > > +    default y
> > > > +    bool "Current frequency derived from HW provided feedback"
> > > > +    help
> > > > +      This determines whether the scaling_cur_freq sysfs attribute returns
> > > > +      the last requested frequency or a more precise value based on hardware
> > > > +      provided feedback (as architected counters).
> > > > +      Given that a more precise frequency can now be provided via the
> > > > +      cpuinfo_avg_cur_freq attribute, by enabling this option,
> > > > +      scaling_cur_freq maintains the provision of a counter based frequency,
> > > > +      for compatibility reasons.
> > > > +
> > > > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> > > > index 04fc786dd2c0..70df2a24437b 100644
> > > > --- a/drivers/cpufreq/cpufreq.c
> > > > +++ b/drivers/cpufreq/cpufreq.c
> > > > @@ -747,9 +747,14 @@ show_one(cpuinfo_transition_latency,
> > > > cpuinfo.transition_latency);
> > > >   show_one(scaling_min_freq, min);
> > > >   show_one(scaling_max_freq, max);
> > > > -__weak unsigned int arch_freq_get_on_cpu(int cpu)
> > > > +__weak int arch_freq_get_on_cpu(int cpu)
> > > >   {
> > > > -    return 0;
> > > > +    return -EOPNOTSUPP;
> > > > +}
> > > > +
> > > > +static inline bool cpufreq_avg_freq_supported(struct cpufreq_policy *policy)
> > > > +{
> > > > +    return arch_freq_get_on_cpu(policy->cpu) != -EOPNOTSUPP;
> > > >   }
> > > >   static ssize_t show_scaling_cur_freq(struct cpufreq_policy *policy, char *buf)
> > > > @@ -757,8 +762,11 @@ static ssize_t show_scaling_cur_freq(struct
> > > > cpufreq_policy *policy, char *buf)
> > > >       ssize_t ret;
> > > >       unsigned int freq;
> > > > -    freq = arch_freq_get_on_cpu(policy->cpu);
> > > > -    if (freq)
> > > > +    freq = IS_ENABLED(CONFIG_CPUFREQ_ARCH_CUR_FREQ)
> > > > +        ? arch_freq_get_on_cpu(policy->cpu)
> > > > +        : 0;
> > > > +
> > > > +    if (freq > 0)
> > > >           ret = sysfs_emit(buf, "%u\n", freq);
> > > >       else if (cpufreq_driver->setpolicy && cpufreq_driver->get)
> > > >           ret = sysfs_emit(buf, "%u\n", cpufreq_driver->get(policy->cpu));
> > > > @@ -802,6 +810,19 @@ static ssize_t show_cpuinfo_cur_freq(struct
> > > > cpufreq_policy *policy,
> > > >       return sysfs_emit(buf, "<unknown>\n");
> > > >   }
> > > > +/*
> > > > + * show_cpuinfo_avg_freq - average CPU frequency as detected by hardware
> > > > + */
> > > > +static ssize_t show_cpuinfo_avg_freq(struct cpufreq_policy *policy,
> > > > +                     char *buf)
> > > > +{
> > > > +    int avg_freq = arch_freq_get_on_cpu(policy->cpu);
> > > 
> > > We are seeing issues when reading cpuinfo_avg_freq on an ARM64 system:
> > > 
> > > $ cat /sys/devices/system/cpu/cpufreq/policy1/cpuinfo_avg_freq
> > > cat: /sys/devices/system/cpu/cpufreq/policy1/cpuinfo_avg_freq:
> > > Resource temporarily unavailable
> > > 
> > > The CPU is in idle state, so arch_freq_get_on_cpu() can't find a
> > > good alternative source for frequency info.
> > > 
> > 
> > Hi Kai Heng,
> > This has already been discussed during v7 in [1] & [2].
> 
> Thanks for the info!
@Sumit: Thank you indeed.
> 
> > In v7, we were returning zero which printed 'unknown'.
> > The discussion was about printing in more descriptive way or with an
> > appropriate error code. In v8 we are returning 'EAGAIN' instead of zero.
> > The final decision was of Maintainers.
> 
> Is there any cpufreq driver that prints "unknown" or error when CPU is in idle?
I think at this point, for cpuinfo_cur_freq, one gets either the frequency value
or 'unknown'. I'm not sure whether there are any drivers that report error upon
'get'.
> 
> I think it's more unsurprising to print the lowest CPU frequency when CPU is
> in idle state, instead of any other error code.
With that approach one cannot easily determine whether the CPU is actually
running at the lowest frequency or it's idle.
Returning an error also avoids mixing types of data provided by the handler.

---
BR
Beata
> 
> Kai-Heng
> 
> > 
> > Viresh,
> > You have any preference on this?
> > 
> > [1] https://lore.kernel.org/lkml/aa254516-968e-4665-bb5b-981c296ffc35@nvidia.com/#t
> > [2] https://lore.kernel.org/lkml/Zyh-uVSW-0d0r8oB@arm.com/
> > 
> > Thank you,
> > Sumit Gupta
> > 
> > > One way to resolve this is to have fallback methods in
> > > show_cpuinfo_avg_freq() so it will look like this:
> > > 
> > > static ssize_t show_cpuinfo_avg_freq(struct cpufreq_policy *policy,
> > >                                       char *buf)
> > > {
> > >          int avg_freq = arch_freq_get_on_cpu(policy->cpu);
> > >          int ret;
> > > 
> > >          if (avg_freq > 0)
> > >                  ret = sysfs_emit(buf, "%u\n", avg_freq);
> > >          else if (cpufreq_driver->setpolicy && cpufreq_driver->get)
> > >                  ret = sysfs_emit(buf, "%u\n", cpufreq_driver->get(policy->cpu));
> > >          else
> > >                  ret = sysfs_emit(buf, "%u\n", policy->cur);
> > >          return ret;
> > > }
> > > 
> > > But that also makes show_cpuinfo_avg_freq() pretty much the same as
> > > show_scaling_cur_freq().
> > > 
> > > So is it possible to consolidate show_cpuinfo_avg_freq() into
> > > show_scaling_cur_freq(), by making CONFIG_CPUFREQ_ARCH_CUR_FREQ also
> > > available to ARM64?
> > > 
> > > Kai-Heng
> > > 
> > > > +
> > > > +    if (avg_freq > 0)
> > > > +        return sysfs_emit(buf, "%u\n", avg_freq);
> > > > +    return avg_freq != 0 ? avg_freq : -EINVAL;
> > > > +}
> > > > +
> > > >   /*
> > > >    * show_scaling_governor - show the current policy for the specified CPU
> > > >    */
> > > > @@ -964,6 +985,7 @@ static ssize_t show_bios_limit(struct
> > > > cpufreq_policy *policy, char *buf)
> > > >   }
> > > >   cpufreq_freq_attr_ro_perm(cpuinfo_cur_freq, 0400);
> > > > +cpufreq_freq_attr_ro(cpuinfo_avg_freq);
> > > >   cpufreq_freq_attr_ro(cpuinfo_min_freq);
> > > >   cpufreq_freq_attr_ro(cpuinfo_max_freq);
> > > >   cpufreq_freq_attr_ro(cpuinfo_transition_latency);
> > > > @@ -1091,6 +1113,12 @@ static int
> > > > cpufreq_add_dev_interface(struct cpufreq_policy *policy)
> > > >               return ret;
> > > >       }
> > > > +    if (cpufreq_avg_freq_supported(policy)) {
> > > > +        ret = sysfs_create_file(&policy->kobj, &cpuinfo_avg_freq.attr);
> > > > +        if (ret)
> > > > +            return ret;
> > > > +    }
> > > > +
> > > >       ret = sysfs_create_file(&policy->kobj, &scaling_cur_freq.attr);
> > > >       if (ret)
> > > >           return ret;
> > > > diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
> > > > index d4d2f4d1d7cb..a7b6c0ccf9bc 100644
> > > > --- a/include/linux/cpufreq.h
> > > > +++ b/include/linux/cpufreq.h
> > > > @@ -1194,7 +1194,7 @@ static inline int
> > > > of_perf_domain_get_sharing_cpumask(int pcpu, const char *list_
> > > >   }
> > > >   #endif
> > > > -extern unsigned int arch_freq_get_on_cpu(int cpu);
> > > > +extern int arch_freq_get_on_cpu(int cpu);
> > > >   #ifndef arch_set_freq_scale
> > > >   static __always_inline
> > > 
> 

Re: [PATCH v8 1/4] cpufreq: Introduce an optional cpuinfo_avg_freq sysfs entry

[Beata Michalska]

On Mon, Dec 16, 2024 at 01:43:02PM +0800, Kai-Heng Feng wrote:
> Hi Beata,
> 
> On 2024/12/6 9:55 PM, Beata Michalska wrote:
> > Currently the CPUFreq core exposes two sysfs attributes that can be used
> > to query current frequency of a given CPU(s): namely cpuinfo_cur_freq
> > and scaling_cur_freq. Both provide slightly different view on the
> > subject and they do come with their own drawbacks.
> > 
> > cpuinfo_cur_freq provides higher precision though at a cost of being
> > rather expensive. Moreover, the information retrieved via this attribute
> > is somewhat short lived as frequency can change at any point of time
> > making it difficult to reason from.
> > 
> > scaling_cur_freq, on the other hand, tends to be less accurate but then
> > the actual level of precision (and source of information) varies between
> > architectures making it a bit ambiguous.
> > 
> > The new attribute, cpuinfo_avg_freq, is intended to provide more stable,
> > distinct interface, exposing an average frequency of a given CPU(s), as
> > reported by the hardware, over a time frame spanning no more than a few
> > milliseconds. As it requires appropriate hardware support, this
> > interface is optional.
> > 
> > Note that under the hood, the new attribute relies on the information
> > provided by arch_freq_get_on_cpu, which, up to this point, has been
> > feeding data for scaling_cur_freq attribute, being the source of
> > ambiguity when it comes to interpretation. This has been amended by
> > restoring the intended behavior for scaling_cur_freq, with a new
> > dedicated config option to maintain status quo for those, who may need
> > it.
> > 
> > CC: Jonathan Corbet <corbet@lwn.net>
> > CC: Thomas Gleixner <tglx@linutronix.de>
> > CC: Ingo Molnar <mingo@redhat.com>
> > CC: Borislav Petkov <bp@alien8.de>
> > CC: Dave Hansen <dave.hansen@linux.intel.com>
> > CC: H. Peter Anvin <hpa@zytor.com>
> > CC: Phil Auld <pauld@redhat.com>
> > CC: x86@kernel.org
> > CC: linux-doc@vger.kernel.org
> > Signed-off-by: Beata Michalska <beata.michalska@arm.com>
> > ---
> >   Documentation/admin-guide/pm/cpufreq.rst | 16 ++++++++++-
> >   arch/x86/kernel/cpu/aperfmperf.c         |  2 +-
> >   arch/x86/kernel/cpu/proc.c               |  7 +++--
> >   drivers/cpufreq/Kconfig.x86              | 12 ++++++++
> >   drivers/cpufreq/cpufreq.c                | 36 +++++++++++++++++++++---
> >   include/linux/cpufreq.h                  |  2 +-
> >   6 files changed, 66 insertions(+), 9 deletions(-)
> > 
> > diff --git a/Documentation/admin-guide/pm/cpufreq.rst b/Documentation/admin-guide/pm/cpufreq.rst
> > index fe1be4ad88cb..76f3835afe01 100644
> > --- a/Documentation/admin-guide/pm/cpufreq.rst
> > +++ b/Documentation/admin-guide/pm/cpufreq.rst
> > @@ -248,6 +248,19 @@ are the following:
> >   	If that frequency cannot be determined, this attribute should not
> >   	be present.
> > +``cpuinfo_avg_freq``
> > +        An average frequency (in KHz) of all CPUs belonging to a given policy,
> > +        derived from a hardware provided feedback and reported on a time frame
> > +        spanning at most few milliseconds.
> > +
> > +        This is expected to be based on the frequency the hardware actually runs
> > +        at and, as such, might require specialised hardware support (such as AMU
> > +        extension on ARM). If one cannot be determined, this attribute should
> > +        not be present.
> > +
> > +        Note, that failed attempt to retrieve current frequency for a given
> > +        CPU(s) will result in an appropriate error.
> > +
> >   ``cpuinfo_max_freq``
> >   	Maximum possible operating frequency the CPUs belonging to this policy
> >   	can run at (in kHz).
> > @@ -293,7 +306,8 @@ are the following:
> >   	Some architectures (e.g. ``x86``) may attempt to provide information
> >   	more precisely reflecting the current CPU frequency through this
> >   	attribute, but that still may not be the exact current CPU frequency as
> > -	seen by the hardware at the moment.
> > +	seen by the hardware at the moment. This behavior though, is only
> > +	available via c:macro:``CPUFREQ_ARCH_CUR_FREQ`` option.
> >   ``scaling_driver``
> >   	The scaling driver currently in use.
> > diff --git a/arch/x86/kernel/cpu/aperfmperf.c b/arch/x86/kernel/cpu/aperfmperf.c
> > index 0b69bfbf345d..a00059139ca4 100644
> > --- a/arch/x86/kernel/cpu/aperfmperf.c
> > +++ b/arch/x86/kernel/cpu/aperfmperf.c
> > @@ -413,7 +413,7 @@ void arch_scale_freq_tick(void)
> >    */
> >   #define MAX_SAMPLE_AGE	((unsigned long)HZ / 50)
> > -unsigned int arch_freq_get_on_cpu(int cpu)
> > +int arch_freq_get_on_cpu(int cpu)
> >   {
> >   	struct aperfmperf *s = per_cpu_ptr(&cpu_samples, cpu);
> >   	unsigned int seq, freq;
> > diff --git a/arch/x86/kernel/cpu/proc.c b/arch/x86/kernel/cpu/proc.c
> > index e65fae63660e..34d8fb93fb70 100644
> > --- a/arch/x86/kernel/cpu/proc.c
> > +++ b/arch/x86/kernel/cpu/proc.c
> > @@ -86,9 +86,12 @@ static int show_cpuinfo(struct seq_file *m, void *v)
> >   		seq_printf(m, "microcode\t: 0x%x\n", c->microcode);
> >   	if (cpu_has(c, X86_FEATURE_TSC)) {
> > -		unsigned int freq = arch_freq_get_on_cpu(cpu);
> > +		int freq = arch_freq_get_on_cpu(cpu);
> > -		seq_printf(m, "cpu MHz\t\t: %u.%03u\n", freq / 1000, (freq % 1000));
> > +		if (freq <= 0)
> > +			seq_puts(m, "cpu MHz\t\t: Unknown\n");
> > +		else
> > +			seq_printf(m, "cpu MHz\t\t: %u.%03u\n", freq / 1000, (freq % 1000));
> >   	}
> >   	/* Cache size */
> > diff --git a/drivers/cpufreq/Kconfig.x86 b/drivers/cpufreq/Kconfig.x86
> > index 97c2d4f15d76..212e1b9afe21 100644
> > --- a/drivers/cpufreq/Kconfig.x86
> > +++ b/drivers/cpufreq/Kconfig.x86
> > @@ -340,3 +340,15 @@ config X86_SPEEDSTEP_RELAXED_CAP_CHECK
> >   	  option lets the probing code bypass some of those checks if the
> >   	  parameter "relaxed_check=1" is passed to the module.
> > +config CPUFREQ_ARCH_CUR_FREQ
> > +	default y
> > +	bool "Current frequency derived from HW provided feedback"
> > +	help
> > +	  This determines whether the scaling_cur_freq sysfs attribute returns
> > +	  the last requested frequency or a more precise value based on hardware
> > +	  provided feedback (as architected counters).
> > +	  Given that a more precise frequency can now be provided via the
> > +	  cpuinfo_avg_cur_freq attribute, by enabling this option,
> > +	  scaling_cur_freq maintains the provision of a counter based frequency,
> > +	  for compatibility reasons.
> > +
> > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> > index 04fc786dd2c0..70df2a24437b 100644
> > --- a/drivers/cpufreq/cpufreq.c
> > +++ b/drivers/cpufreq/cpufreq.c
> > @@ -747,9 +747,14 @@ show_one(cpuinfo_transition_latency, cpuinfo.transition_latency);
> >   show_one(scaling_min_freq, min);
> >   show_one(scaling_max_freq, max);
> > -__weak unsigned int arch_freq_get_on_cpu(int cpu)
> > +__weak int arch_freq_get_on_cpu(int cpu)
> >   {
> > -	return 0;
> > +	return -EOPNOTSUPP;
> > +}
> > +
> > +static inline bool cpufreq_avg_freq_supported(struct cpufreq_policy *policy)
> > +{
> > +	return arch_freq_get_on_cpu(policy->cpu) != -EOPNOTSUPP;
> >   }
> >   static ssize_t show_scaling_cur_freq(struct cpufreq_policy *policy, char *buf)
> > @@ -757,8 +762,11 @@ static ssize_t show_scaling_cur_freq(struct cpufreq_policy *policy, char *buf)
> >   	ssize_t ret;
> >   	unsigned int freq;
> > -	freq = arch_freq_get_on_cpu(policy->cpu);
> > -	if (freq)
> > +	freq = IS_ENABLED(CONFIG_CPUFREQ_ARCH_CUR_FREQ)
> > +		? arch_freq_get_on_cpu(policy->cpu)
> > +		: 0;
> > +
> > +	if (freq > 0)
> >   		ret = sysfs_emit(buf, "%u\n", freq);
> >   	else if (cpufreq_driver->setpolicy && cpufreq_driver->get)
> >   		ret = sysfs_emit(buf, "%u\n", cpufreq_driver->get(policy->cpu));
> > @@ -802,6 +810,19 @@ static ssize_t show_cpuinfo_cur_freq(struct cpufreq_policy *policy,
> >   	return sysfs_emit(buf, "<unknown>\n");
> >   }
> > +/*
> > + * show_cpuinfo_avg_freq - average CPU frequency as detected by hardware
> > + */
> > +static ssize_t show_cpuinfo_avg_freq(struct cpufreq_policy *policy,
> > +				     char *buf)
> > +{
> > +	int avg_freq = arch_freq_get_on_cpu(policy->cpu);
> 
> We are seeing issues when reading cpuinfo_avg_freq on an ARM64 system:
> 
> $ cat /sys/devices/system/cpu/cpufreq/policy1/cpuinfo_avg_freq
> cat: /sys/devices/system/cpu/cpufreq/policy1/cpuinfo_avg_freq: Resource
> temporarily unavailable
> 
> The CPU is in idle state, so arch_freq_get_on_cpu() can't find a good
> alternative source for frequency info.
> 
> One way to resolve this is to have fallback methods in
> show_cpuinfo_avg_freq() so it will look like this:
> 
> static ssize_t show_cpuinfo_avg_freq(struct cpufreq_policy *policy,
>                                      char *buf)
> {
>         int avg_freq = arch_freq_get_on_cpu(policy->cpu);
>         int ret;
> 
>         if (avg_freq > 0)
>                 ret = sysfs_emit(buf, "%u\n", avg_freq);
>         else if (cpufreq_driver->setpolicy && cpufreq_driver->get)
>                 ret = sysfs_emit(buf, "%u\n", cpufreq_driver->get(policy->cpu));
>         else
>                 ret = sysfs_emit(buf, "%u\n", policy->cur);
>         return ret;
> }
> 
> But that also makes show_cpuinfo_avg_freq() pretty much the same as
> show_scaling_cur_freq().
> 
> So is it possible to consolidate show_cpuinfo_avg_freq() into
> show_scaling_cur_freq(), by making CONFIG_CPUFREQ_ARCH_CUR_FREQ also
> available to ARM64?
>
The whole idea of this patch was to add support for retrieving the average
frequency withouth modifying expected bahaviour of the scaling_cur_freq handler.
The proposed config option is there to keep backward compatibility and allow
userspace tools to catch up with the change - I'd expect that option to be
either set as default to No or droped at some point.

---
BR
Beata
> Kai-Heng
> 
> > +
> > +	if (avg_freq > 0)
> > +		return sysfs_emit(buf, "%u\n", avg_freq);
> > +	return avg_freq != 0 ? avg_freq : -EINVAL;
> > +}
> > +
> >   /*
> >    * show_scaling_governor - show the current policy for the specified CPU
> >    */
> > @@ -964,6 +985,7 @@ static ssize_t show_bios_limit(struct cpufreq_policy *policy, char *buf)
> >   }
> >   cpufreq_freq_attr_ro_perm(cpuinfo_cur_freq, 0400);
> > +cpufreq_freq_attr_ro(cpuinfo_avg_freq);
> >   cpufreq_freq_attr_ro(cpuinfo_min_freq);
> >   cpufreq_freq_attr_ro(cpuinfo_max_freq);
> >   cpufreq_freq_attr_ro(cpuinfo_transition_latency);
> > @@ -1091,6 +1113,12 @@ static int cpufreq_add_dev_interface(struct cpufreq_policy *policy)
> >   			return ret;
> >   	}
> > +	if (cpufreq_avg_freq_supported(policy)) {
> > +		ret = sysfs_create_file(&policy->kobj, &cpuinfo_avg_freq.attr);
> > +		if (ret)
> > +			return ret;
> > +	}
> > +
> >   	ret = sysfs_create_file(&policy->kobj, &scaling_cur_freq.attr);
> >   	if (ret)
> >   		return ret;
> > diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
> > index d4d2f4d1d7cb..a7b6c0ccf9bc 100644
> > --- a/include/linux/cpufreq.h
> > +++ b/include/linux/cpufreq.h
> > @@ -1194,7 +1194,7 @@ static inline int of_perf_domain_get_sharing_cpumask(int pcpu, const char *list_
> >   }
> >   #endif
> > -extern unsigned int arch_freq_get_on_cpu(int cpu);
> > +extern int arch_freq_get_on_cpu(int cpu);
> >   #ifndef arch_set_freq_scale
> >   static __always_inline
> 

[PATCH v8 2/4] arm64: amu: Delay allocating cpumask for AMU FIE support

[Beata Michalska]

For the time being, the amu_fie_cpus cpumask is being exclusively used
by the AMU-related internals of FIE support and is guaranteed to be
valid on every access currently made. Still the mask is not being
invalidated on one of the error handling code paths, which leaves
a soft spot with theoretical risk of UAF for CPUMASK_OFFSTACK cases.
To make things sound, delay allocating said cpumask
(for CPUMASK_OFFSTACK) avoiding otherwise nasty sanitising case failing
to register the cpufreq policy notifications.

Signed-off-by: Beata Michalska <beata.michalska@arm.com>
---
 arch/arm64/kernel/topology.c | 22 ++++++++++------------
 1 file changed, 10 insertions(+), 12 deletions(-)

diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
index 1a2c72f3e7f8..cb180684d10d 100644
--- a/arch/arm64/kernel/topology.c
+++ b/arch/arm64/kernel/topology.c
@@ -194,12 +194,19 @@ static void amu_fie_setup(const struct cpumask *cpus)
 	int cpu;
 
 	/* We are already set since the last insmod of cpufreq driver */
-	if (unlikely(cpumask_subset(cpus, amu_fie_cpus)))
+	if (cpumask_available(amu_fie_cpus) &&
+	    unlikely(cpumask_subset(cpus, amu_fie_cpus)))
 		return;
 
-	for_each_cpu(cpu, cpus) {
+	for_each_cpu(cpu, cpus)
 		if (!freq_counters_valid(cpu))
 			return;
+
+	if (!cpumask_available(amu_fie_cpus) &&
+	    !zalloc_cpumask_var(&amu_fie_cpus, GFP_KERNEL)) {
+		WARN_ONCE(1, "Failed to allocate FIE cpumask for CPUs[%*pbl]\n",
+			  cpumask_pr_args(cpus));
+		return;
 	}
 
 	cpumask_or(amu_fie_cpus, amu_fie_cpus, cpus);
@@ -237,17 +244,8 @@ static struct notifier_block init_amu_fie_notifier = {
 
 static int __init init_amu_fie(void)
 {
-	int ret;
-
-	if (!zalloc_cpumask_var(&amu_fie_cpus, GFP_KERNEL))
-		return -ENOMEM;
-
-	ret = cpufreq_register_notifier(&init_amu_fie_notifier,
+	return cpufreq_register_notifier(&init_amu_fie_notifier,
 					CPUFREQ_POLICY_NOTIFIER);
-	if (ret)
-		free_cpumask_var(amu_fie_cpus);
-
-	return ret;
 }
 core_initcall(init_amu_fie);
 
-- 
2.25.1

[PATCH v8 3/4] arm64: Provide an AMU-based version of arch_freq_get_on_cpu

[Beata Michalska]

With the Frequency Invariance Engine (FIE) being already wired up with
sched tick and making use of relevant (core counter and constant
counter) AMU counters, getting the average frequency for a given CPU,
can be achieved by utilizing the frequency scale factor which reflects
an average CPU frequency for the last tick period length.

The solution is partially based on APERF/MPERF implementation of
arch_freq_get_on_cpu.

Suggested-by: Ionela Voinescu <ionela.voinescu@arm.com>
Signed-off-by: Beata Michalska <beata.michalska@arm.com>
---
 arch/arm64/kernel/topology.c | 109 +++++++++++++++++++++++++++++++----
 1 file changed, 99 insertions(+), 10 deletions(-)

diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
index cb180684d10d..5f5738b174c7 100644
--- a/arch/arm64/kernel/topology.c
+++ b/arch/arm64/kernel/topology.c
@@ -17,6 +17,7 @@
 #include <linux/cpufreq.h>
 #include <linux/init.h>
 #include <linux/percpu.h>
+#include <linux/sched/isolation.h>
 
 #include <asm/cpu.h>
 #include <asm/cputype.h>
@@ -88,18 +89,28 @@ int __init parse_acpi_topology(void)
  * initialized.
  */
 static DEFINE_PER_CPU_READ_MOSTLY(unsigned long, arch_max_freq_scale) =  1UL << (2 * SCHED_CAPACITY_SHIFT);
-static DEFINE_PER_CPU(u64, arch_const_cycles_prev);
-static DEFINE_PER_CPU(u64, arch_core_cycles_prev);
 static cpumask_var_t amu_fie_cpus;
 
+struct amu_cntr_sample {
+	u64		arch_const_cycles_prev;
+	u64		arch_core_cycles_prev;
+	unsigned long	last_scale_update;
+};
+
+static DEFINE_PER_CPU_SHARED_ALIGNED(struct amu_cntr_sample, cpu_amu_samples);
+
 void update_freq_counters_refs(void)
 {
-	this_cpu_write(arch_core_cycles_prev, read_corecnt());
-	this_cpu_write(arch_const_cycles_prev, read_constcnt());
+	struct amu_cntr_sample *amu_sample = this_cpu_ptr(&cpu_amu_samples);
+
+	amu_sample->arch_core_cycles_prev = read_corecnt();
+	amu_sample->arch_const_cycles_prev = read_constcnt();
 }
 
 static inline bool freq_counters_valid(int cpu)
 {
+	struct amu_cntr_sample *amu_sample = per_cpu_ptr(&cpu_amu_samples, cpu);
+
 	if ((cpu >= nr_cpu_ids) || !cpumask_test_cpu(cpu, cpu_present_mask))
 		return false;
 
@@ -108,8 +119,8 @@ static inline bool freq_counters_valid(int cpu)
 		return false;
 	}
 
-	if (unlikely(!per_cpu(arch_const_cycles_prev, cpu) ||
-		     !per_cpu(arch_core_cycles_prev, cpu))) {
+	if (unlikely(!amu_sample->arch_const_cycles_prev ||
+		     !amu_sample->arch_core_cycles_prev)) {
 		pr_debug("CPU%d: cycle counters are not enabled.\n", cpu);
 		return false;
 	}
@@ -152,17 +163,22 @@ void freq_inv_set_max_ratio(int cpu, u64 max_rate)
 
 static void amu_scale_freq_tick(void)
 {
+	struct amu_cntr_sample *amu_sample = this_cpu_ptr(&cpu_amu_samples);
 	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);
+	prev_const_cnt = amu_sample->arch_const_cycles_prev;
+	prev_core_cnt = amu_sample->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);
+	const_cnt = amu_sample->arch_const_cycles_prev;
+	core_cnt = amu_sample->arch_core_cycles_prev;
 
+	/*
+	 * This should not happen unless the AMUs have been reset and the
+	 * counter values have not been restored - unlikely
+	 */
 	if (unlikely(core_cnt <= prev_core_cnt ||
 		     const_cnt <= prev_const_cnt))
 		return;
@@ -182,6 +198,8 @@ static void amu_scale_freq_tick(void)
 
 	scale = min_t(unsigned long, scale, SCHED_CAPACITY_SCALE);
 	this_cpu_write(arch_freq_scale, (unsigned long)scale);
+
+	amu_sample->last_scale_update = jiffies;
 }
 
 static struct scale_freq_data amu_sfd = {
@@ -189,6 +207,77 @@ static struct scale_freq_data amu_sfd = {
 	.set_freq_scale = amu_scale_freq_tick,
 };
 
+static __always_inline bool amu_fie_cpu_supported(unsigned int cpu)
+{
+	return cpumask_available(amu_fie_cpus) &&
+		cpumask_test_cpu(cpu, amu_fie_cpus);
+}
+
+#define AMU_SAMPLE_EXP_MS	20
+
+int arch_freq_get_on_cpu(int cpu)
+{
+	struct amu_cntr_sample *amu_sample;
+	unsigned int start_cpu = cpu;
+	unsigned long last_update;
+	unsigned int freq = 0;
+	u64 scale;
+
+	if (!amu_fie_cpu_supported(cpu) || !arch_scale_freq_ref(cpu))
+		return -EOPNOTSUPP;
+
+retry:
+	amu_sample = per_cpu_ptr(&cpu_amu_samples, cpu);
+
+	last_update = amu_sample->last_scale_update;
+
+	/*
+	 * For those CPUs that are in full dynticks mode, or those that have
+	 * not seen tick for a while, try an alternative source for the counters
+	 * (and thus freq scale), if available, for given policy: this boils
+	 * down to identifying an active cpu within the same freq domain, if any.
+	 */
+	if (!housekeeping_cpu(cpu, HK_TYPE_TICK) ||
+	    time_is_before_jiffies(last_update + msecs_to_jiffies(AMU_SAMPLE_EXP_MS))) {
+		struct cpufreq_policy *policy = cpufreq_cpu_get(cpu);
+		int ref_cpu = cpu;
+
+		if (!policy)
+			return -EINVAL;
+
+		if (!cpumask_intersects(policy->related_cpus,
+					housekeeping_cpumask(HK_TYPE_TICK))) {
+			cpufreq_cpu_put(policy);
+			return -EOPNOTSUPP;
+		}
+
+
+		do {
+			ref_cpu = cpumask_next_wrap(ref_cpu, policy->cpus,
+						    start_cpu, false);
+
+		} while (ref_cpu < nr_cpu_ids && idle_cpu(ref_cpu));
+
+		cpufreq_cpu_put(policy);
+
+		if (ref_cpu >= nr_cpu_ids)
+			/* No alternative to pull info from */
+			return -EAGAIN;
+
+		cpu = ref_cpu;
+		goto retry;
+	}
+	/*
+	 * Reversed computation to the one used to determine
+	 * the arch_freq_scale value
+	 * (see amu_scale_freq_tick for details)
+	 */
+	scale = arch_scale_freq_capacity(cpu);
+	freq = scale * arch_scale_freq_ref(cpu);
+	freq >>= SCHED_CAPACITY_SHIFT;
+	return freq;
+}
+
 static void amu_fie_setup(const struct cpumask *cpus)
 {
 	int cpu;
-- 
2.25.1

[PATCH v8 4/4] arm64: Update AMU-based freq scale factor on entering idle

[Beata Michalska]

Now that the frequency scale factor has been activated for retrieving
current frequency on a given CPU, trigger its update upon entering
idle. This will, to an extent, allow querying last known frequency
in a non-invasive way. It will also improve the frequency scale factor
accuracy when a CPU entering idle did not receive a tick for a while.
As a consequence, for idle cores, the reported frequency will be the
last one observed before entering the idle state.

Suggested-by: Vanshidhar Konda <vanshikonda@os.amperecomputing.com>
Signed-off-by: Beata Michalska <beata.michalska@arm.com>
---
 arch/arm64/kernel/topology.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
index 5f5738b174c7..6c43aafac77c 100644
--- a/arch/arm64/kernel/topology.c
+++ b/arch/arm64/kernel/topology.c
@@ -213,6 +213,19 @@ static __always_inline bool amu_fie_cpu_supported(unsigned int cpu)
 		cpumask_test_cpu(cpu, amu_fie_cpus);
 }
 
+void arch_cpu_idle_enter(void)
+{
+	unsigned int cpu = smp_processor_id();
+
+	if (!amu_fie_cpu_supported(cpu))
+		return;
+
+	/* Kick in AMU update but only if one has not happened already */
+	if (housekeeping_cpu(cpu, HK_TYPE_TICK) &&
+	    time_is_before_jiffies(per_cpu(cpu_amu_samples.last_scale_update, cpu)))
+		amu_scale_freq_tick();
+}
+
 #define AMU_SAMPLE_EXP_MS	20
 
 int arch_freq_get_on_cpu(int cpu)
-- 
2.25.1