Our H8SGL-F MB with AMD Opteron 6212 (reference: OS6212WKT8GGU) CPU cache will show up as 12MB L3 cache instead of 16MB.
As per this CPU specs, it is a 16MB L3 cache, any idea?
The 6212 CPU is 16MB cache and it will show up as 12 MB because of "HT Assist" feature for Opteron 6200 and 6300 CPUs. This feature will lock part of the L3 cache for internal operations, and 4MB is used for the probe filter was an expected behavior.
Abu Dhabi (6300): 16MB physical L3 | 12MB OS-useable L3
AS per AMD:
"HT Assist, or the Probe Filter as it is sometimes called, works by using part of the processor’s L3 cache as a directory cache. This directory cache tracks all cache lines cached in the system. Instead of generating numerous cache probes when checking a cache line the processor does a Probe Filter Lookup. This helps lower latency for accesses to local DRAM because there is no need to wait for probe responses when accessing local data. This also means there is less queuing delay due to the lower Hyper Transport technology traffic."
This features can shorten the memory access time and increase the bandwidth.