Use AIX nmon to display L1 and L2 cache size on Power

Here’s a great little tip from Carl Burnett (Distinguished Engineer, IBM Power Systems SW Development).

Q: Is there a command or method to provide the size of the processor's L1/L2 cache under the E1080+AIX environment? A customer wants to verify the contents of a datasheet on their system.

A: nmon -q can be used to get L1/L2

# nmon -q

CPU Type Architecture=PowerPC Implementation=POWER10

64 bit CPU

16 CPUs on startup

16 CPUs now

CPU Level 1 Cache is Combined Instruction=49152 bytes & Data=32768 bytes

CPU Level 2 Cache size=1048576

CHRP=Common H/W Reference Platform Hardware-Arch(NIM)

PCI Bus-Type

Multi-Processor 64 bit Kernel

Logical partition =Dynamic

AIX 7.3.2.2 TL02

SerialNumber 1365AF9

myaixvm.aus.stglabs.ibm.com hostname

myaixvm uname

# lsconf | grep "System Model"

System Model: IBM,9080-HEX

Note: The Power10 chip does have 2M total of L2 cache for each core as documented in the Redbook. The reason the tooling displays the L2 cache size only shows 1M for the L2 cache size is that the L2 cache is split into 2 different halves where half the threads on the core use one half and the other threads use the other half. So any given thread only has use of half the L2 (1M). The interfaces commands (like nmon) use to get the L2 cache size are also intended for code optimization purposes, which is why they display just what is accessible to any given thread on the core.