MPAM needs to know the size of a cache associated with a particular CPU.
The DT/ACPI agnostic way of doing this is to ask cacheinfo.

Add a helper to do this.

Signed-off-by: James Morse <james.morse@arm.com>

---
Changes since v1:
 * Converted to kdoc.
 * Simplified helper to use get_cpu_cacheinfo_level().
---
 include/linux/cacheinfo.h | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/include/linux/cacheinfo.h b/include/linux/cacheinfo.h
index 2dcbb69139e9..e12d6f2c6a57 100644
--- a/include/linux/cacheinfo.h
+++ b/include/linux/cacheinfo.h
@@ -148,6 +148,21 @@ static inline int get_cpu_cacheinfo_id(int cpu, int level)
 	return ci ? ci->id : -1;
 }
 
+/**
+ * get_cpu_cacheinfo_size() - Get the size of the cache.
+ * @cpu:      The cpu that is associated with the cache.
+ * @level:    The level of the cache as seen by @cpu.
+ *
+ * Callers must hold the cpuhp lock.
+ * Returns the cache-size on success, or 0 for an error.
+ */
+static inline unsigned int get_cpu_cacheinfo_size(int cpu, int level)
+{
+	struct cacheinfo *ci = get_cpu_cacheinfo_level(cpu, level);
+
+	return ci ? ci->size : 0;
+}
+
 #if defined(CONFIG_ARM64) || defined(CONFIG_ARM)
 #define use_arch_cache_info()	(true)
 #else
-- 
2.20.1

Hi,

On Fri, Aug 22, 2025 at 03:29:43PM +0000, James Morse wrote:
> MPAM needs to know the size of a cache associated with a particular CPU.
> The DT/ACPI agnostic way of doing this is to ask cacheinfo.
> 
> Add a helper to do this.
> 
> Signed-off-by: James Morse <james.morse@arm.com>
> 
> ---
> Changes since v1:
>  * Converted to kdoc.
>  * Simplified helper to use get_cpu_cacheinfo_level().
> ---
>  include/linux/cacheinfo.h | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/include/linux/cacheinfo.h b/include/linux/cacheinfo.h
> index 2dcbb69139e9..e12d6f2c6a57 100644
> --- a/include/linux/cacheinfo.h
> +++ b/include/linux/cacheinfo.h
> @@ -148,6 +148,21 @@ static inline int get_cpu_cacheinfo_id(int cpu, int level)
>  	return ci ? ci->id : -1;
>  }
>  
> +/**
> + * get_cpu_cacheinfo_size() - Get the size of the cache.
> + * @cpu:      The cpu that is associated with the cache.
> + * @level:    The level of the cache as seen by @cpu.
> + *
> + * Callers must hold the cpuhp lock.
> + * Returns the cache-size on success, or 0 for an error.
> + */

Nit: Maybe use the wording

	cpuhp lock must be held.

in the kerneldoc here, to match the other helpers it sits alongside.

Otherwise, looks reasonable.

> +static inline unsigned int get_cpu_cacheinfo_size(int cpu, int level)
> +{
> +	struct cacheinfo *ci = get_cpu_cacheinfo_level(cpu, level);
> +
> +	return ci ? ci->size : 0;
> +}
> +

Orphaned function?

Can fs/resctrl/rdtgroup.c:rdtgroup_cbm_to_size() be ported to use this?
If so, this wouldn't just be dead code in this series.

Cheers
---Dave

Hi Dave,

On 27/08/2025 11:46, Dave Martin wrote:
> Hi,
> 
> On Fri, Aug 22, 2025 at 03:29:43PM +0000, James Morse wrote:
>> MPAM needs to know the size of a cache associated with a particular CPU.
>> The DT/ACPI agnostic way of doing this is to ask cacheinfo.
>>
>> Add a helper to do this.

>> diff --git a/include/linux/cacheinfo.h b/include/linux/cacheinfo.h
>> index 2dcbb69139e9..e12d6f2c6a57 100644
>> --- a/include/linux/cacheinfo.h
>> +++ b/include/linux/cacheinfo.h
>> @@ -148,6 +148,21 @@ static inline int get_cpu_cacheinfo_id(int cpu, int level)
>>  	return ci ? ci->id : -1;
>>  }
>>  
>> +/**
>> + * get_cpu_cacheinfo_size() - Get the size of the cache.
>> + * @cpu:      The cpu that is associated with the cache.
>> + * @level:    The level of the cache as seen by @cpu.
>> + *
>> + * Callers must hold the cpuhp lock.
>> + * Returns the cache-size on success, or 0 for an error.
>> + */
> 
> Nit: Maybe use the wording
> 
> 	cpuhp lock must be held.
> 
> in the kerneldoc here, to match the other helpers it sits alongside.
> 
> Otherwise, looks reasonable.

Sure,


>> +static inline unsigned int get_cpu_cacheinfo_size(int cpu, int level)
>> +{
>> +	struct cacheinfo *ci = get_cpu_cacheinfo_level(cpu, level);
>> +
>> +	return ci ? ci->size : 0;
>> +}
>> +
> 
> Orphaned function?
> 
> Can fs/resctrl/rdtgroup.c:rdtgroup_cbm_to_size() be ported to use this?
> If so, this wouldn't just be dead code in this series.

Ah - I thought the MPAM driver was pulling this value in, but its the resctrl glue code.
I was trying to reduce the number of trees this touches - its probably best to kick this
into the next series that adds the resctrl code as its pretty trivial.


Thanks,

James

Hi,

On Wed, Aug 27, 2025 at 06:11:43PM +0100, James Morse wrote:
> Hi Dave,
> 
> On 27/08/2025 11:46, Dave Martin wrote:
> > Hi,
> > 
> > On Fri, Aug 22, 2025 at 03:29:43PM +0000, James Morse wrote:
> >> MPAM needs to know the size of a cache associated with a particular CPU.
> >> The DT/ACPI agnostic way of doing this is to ask cacheinfo.
> >>
> >> Add a helper to do this.
> 
> >> diff --git a/include/linux/cacheinfo.h b/include/linux/cacheinfo.h

[...]

> >> +static inline unsigned int get_cpu_cacheinfo_size(int cpu, int level)
> >> +{
> >> +	struct cacheinfo *ci = get_cpu_cacheinfo_level(cpu, level);
> >> +
> >> +	return ci ? ci->size : 0;
> >> +}
> >> +
> > 
> > Orphaned function?
> > 
> > Can fs/resctrl/rdtgroup.c:rdtgroup_cbm_to_size() be ported to use this?
> > If so, this wouldn't just be dead code in this series.
> 
> Ah - I thought the MPAM driver was pulling this value in, but its the resctrl glue code.
> I was trying to reduce the number of trees this touches - its probably best to kick this
> into the next series that adds the resctrl code as its pretty trivial.
> 
> 
> Thanks,
> 
> James
> 

Fair enough.

Cheers
---Dave

Hi James,

On Wed, Aug 27, 2025 at 06:11:43PM +0100, James Morse wrote:
> Hi Dave,
> 
> On 27/08/2025 11:46, Dave Martin wrote:
> > Hi,
> > 
> > On Fri, Aug 22, 2025 at 03:29:43PM +0000, James Morse wrote:
> >> MPAM needs to know the size of a cache associated with a particular CPU.
> >> The DT/ACPI agnostic way of doing this is to ask cacheinfo.
> >>
> >> Add a helper to do this.
> 
> >> diff --git a/include/linux/cacheinfo.h b/include/linux/cacheinfo.h
> >> index 2dcbb69139e9..e12d6f2c6a57 100644
> >> --- a/include/linux/cacheinfo.h
> >> +++ b/include/linux/cacheinfo.h
> >> @@ -148,6 +148,21 @@ static inline int get_cpu_cacheinfo_id(int cpu, int level)
> >>  	return ci ? ci->id : -1;
> >>  }
> >>  
> >> +/**
> >> + * get_cpu_cacheinfo_size() - Get the size of the cache.
> >> + * @cpu:      The cpu that is associated with the cache.
> >> + * @level:    The level of the cache as seen by @cpu.
> >> + *
> >> + * Callers must hold the cpuhp lock.
> >> + * Returns the cache-size on success, or 0 for an error.
> >> + */
> > 
> > Nit: Maybe use the wording
> > 
> > 	cpuhp lock must be held.
> > 
> > in the kerneldoc here, to match the other helpers it sits alongside.
> > 
> > Otherwise, looks reasonable.
> 
> Sure,
> 
> 
> >> +static inline unsigned int get_cpu_cacheinfo_size(int cpu, int level)
> >> +{
> >> +	struct cacheinfo *ci = get_cpu_cacheinfo_level(cpu, level);
> >> +
> >> +	return ci ? ci->size : 0;
> >> +}
> >> +
> > 
> > Orphaned function?
> > 
> > Can fs/resctrl/rdtgroup.c:rdtgroup_cbm_to_size() be ported to use this?
> > If so, this wouldn't just be dead code in this series.
> 
> Ah - I thought the MPAM driver was pulling this value in, but its the resctrl glue code.
> I was trying to reduce the number of trees this touches - its probably best to kick this
> into the next series that adds the resctrl code as its pretty trivial.
> 
> 
> Thanks,
> 
> James

Sure, that also works.

Cheers
---Dave

On 22/08/2025 17:29, James Morse wrote:
> MPAM needs to know the size of a cache associated with a particular CPU.
> The DT/ACPI agnostic way of doing this is to ask cacheinfo.
> 
> Add a helper to do this.
> 
> Signed-off-by: James Morse <james.morse@arm.com>
> 
> ---
> Changes since v1:

You marked this as v1.

>  * Converted to kdoc.
>  * Simplified helper to use get_cpu_cacheinfo_level().
Please use consistent subject prefixes. Look at previous patch subject
prefix.

Best regards,
Krzysztof

Hi Krzysztof,

On 24/08/2025 18:25, Krzysztof Kozlowski wrote:
> On 22/08/2025 17:29, James Morse wrote:
>> MPAM needs to know the size of a cache associated with a particular CPU.
>> The DT/ACPI agnostic way of doing this is to ask cacheinfo.
>>
>> Add a helper to do this.

>> ---
>> Changes since v1:
> 
> You marked this as v1.

Oops - that should say RFC. I'll fix all those.


>>  * Converted to kdoc.
>>  * Simplified helper to use get_cpu_cacheinfo_level().

> Please use consistent subject prefixes. Look at previous patch subject
> prefix.

Presumably the previous patch in my series - this is a side effect of multiple branches
that were written at different times getting combined! I'll change it to 'cacheinfo:' as
that seems to be the most popular recently.


Thanks,

James