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:

quoted

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.

quoted

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,

quoted

+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