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I will greatly appreciate any help regarding the following matters:
(1) How to know whether my machine is NUMA-aware or not,
(2) Difference between memory bank interleaving and node interleaving
(3) When the BIOS asks me to set bank interleaving as AUTO, then it says that AUTO allows memory access to spread out over banks on the same node or across nodes decreasing memory access contentions. However, I have no idea when the memory access is spread over banks on the same node or across nodes. I also do not know how to tell the machine to access memory across the nodes or on the same node. I have no idea as to how the AUTO choice affects NUMA-awareness.
(4) The BIOS also tells me that I could choose bani interleaving as DISABLED. But I do not know what its implications are for NUMA awareness.
Here are other relevant details. I have a dual-Opteron 250 (2.4GHz) set in Tyan Thunder 2885 K8W with AMIBIOS version 2.05.
When I bought it last year, the machine was running under SuSE 9.1 Pro and the Linux kernel was 2.6.5-7.108-smp. At that time both the Hardware Info from YAST and /vat/log/messages were explicitly mentioning things :
Scanning NUMA topology in Northbridge 24
<6>Number of nodes 2 (10010)
<6>Node 0 MemBase 0000000000000000 Limit 000000007fffffff
<6>Node 1 MemBase 0000000080000000 Limit 00000000cbff0000
<6>Using node hash shift of 24
These messages indicated that NODE interleaving was off and the machine was NUMA-aware.
Then, after a few months, the motherboard failed and the machine was sent to the vendor for repair. It came back with SuSE 9.3 and the Linux kernel version 126.96.36.199-21.7-smp (geeko@buildhost) (gcc version 3.3.5 20050117 (prerelease) (SUSE Linux)) #1 SMP Thu Jun 2 14:23:14 UTC 2005.
Now both the Hardware Info from YAST and /vat/log/messages DO NOT mention NUMA anywhere, and I do not have anyway to check whether the NODE-Interleaving is OFF or ON. My difficulties are compounded because I do not know how to interpret the chipset related setting in the BIOS.
Currently, in the BIOS setting (Chipset->memory config -> Bank Interleaving), I am asked to choose between AUTO & DISABLED. No choice is offered for Node Interleaving.
The only guidance for the choice is that interleaving allows memory access to spread out over banks on the same node or across nodes decreasing memory access contentions. Nothing is mentioned about what happens when Interleaving is disabled. Furthermore, if I choose AUTO, then I do not know when the memory is spread out over banks on the same node or across nodes.
I'm not sure what "node" refers to in this context, but memory interleaving works very similarly to RAID0. Rather than addressing memory sequentially, the BIOS will stripe the addresses across the modules. Other than the rather modest 5%-10% performance gain, disabling interleaving shouldn't affect anything. As far as I know it should be completely transparent to the OS too -- Linux doesn't need to be told whether it's enabled or disabled.