Bug 207685

Summary: [ARM64] different CPU L3 cache size reported by /sys/device/ and dmidecode
Product: ACPI Reporter: Aaron Chou (zhoubb.aaron)
Component: Config-ProcessorsAssignee: acpi_config-processors
Status: RESOLVED WILL_NOT_FIX    
Severity: normal    
Priority: P1    
Hardware: ARM   
OS: Linux   
Kernel Version: 4.19.90 Subsystem:
Regression: No Bisected commit-id:

Description Aaron Chou 2020-05-11 06:54:03 UTC 
In the system, I can get the L3 cache size from two or more ways.

Firstly, I can get it from the kernel interface, such as the `lscpu` command.
Also, I can cat the file `/sys/devices/system/cpu/cpu3/cache/index3/size`.

The way above can give me the L3 cache size is 32768K.

Now if I use the `dmidecode -t cache` command, I get the L3 cache size is 24576K.

And the real size of the L3 cache is 24576K.

Why is it? who can explain it to me?

Thanks.
Comment 1 Aaron Chou 2020-05-11 08:41:27 UTC 
ACPI reads these cache information from PPTT. The firmware which populates
the ACPI PPTT must read it from DMI entries and keep them in sync. On
this system, looks like the firmware tried to be more imaginative and
populated PPTT with wrong values. Get that firmware fixed please!

Answered by Sudeep Holla!