Dual Core CPU with VPar/PRM

[techuser_1]

When using Dual Core processors with vpars do you lose any benefit of the shared resources? What about when you designate an uneven number of processors?

Basically I'd like to know:
How to tell where the logical CPU is located on a physical CPU? I'd like to be able to make sure that I'm not hurting performance by splitting dual cores. How to verify this?

[Steven E. Protter]

Shalom,

A Dual Core processor is one CPU to the operating system. You can not as far as I can tell dedicate one of the processors built into a single dual core die to more than one vpar.

This is for all intents and purposes a single CPU to the OS. Because it does have two physical CPU's it does do its work very quickly.

OS's other than HP-UX may react differently. Linux for exanple does recognize two CPU's in a dual core. Linux does not contain a product like vpar's however so the comparison only goes so far.

SEP

[Duncan Edmonstone · Accepted solution]

Steven,

I'm really not sure what your are referring to stating that a dual-core CPU is a single CPU to the OS. This isn't the case - if I have a system with 2 dual-core PA8900 processor modules, then I have 4 CPU cores and HP-UX will see 4 CPUs (you can check with ioscan), and naturally I will see 4 run queues.

To answer the original question, the following are quotations from the vPar user guide:

http://docs.hp.com/en/T1335-90051/T1335-90051.pdf

-----------------
vparstatus: dual-core CPUs

You can see the sibling and virtual partition assignment using vparstatus -d. If you do not have a dual-core system, the output will show dashes (-) for the sibling and assignment information:

# vparstatus -d
CPU Cell Config Sibling Information
path CPU HPA ID Status Assigned to Path /vPar name
===== ================== ==== ====== ================== =======================
0.10 0xfffffffffc078000 0 E vpuma02 - -
0.11 0xfffffffffc07a000 0 E vpuma01 - -
0.12 0xfffffffffc07c000 0 E vpuma04 - -
0.13 0xfffffffffc07e000 0 E - - -
...

When you do have dual-core system, the vparstatus -d output will look similar to the following:

# vparstatus -d
CPU Cell Config Sibling Information
path CPU HPA ID Status Assigned to Path /vPar name
===== ================== ==== ====== ================== =======================
0.10 0xfffffffffc070000 0 E vpkeira1 0.11 vpkeira3
0.11 0xfffffffffc071000 0 E vpkeira3 0.10 vpkeira1
0.12 0xfffffffffc074000 0 E - 0.13 vpkeira4
0.13 0xfffffffffc075000 0 E vpkeira4 0.12 -
0.14 0xfffffffffc078000 0 E - 0.15 -
0.15 0xfffffffffc079000 0 E - 0.14 -
...

-----------------

Splitting sibling CPUs across virtual partition refers to assigning one sibling CPU to one partition and assigning the other sibling CPU to a different virtual partition. No noticeable performance degradation has been seen when splitting sibling CPUs. Due to items such as the larger L2 cache size, there actually can be a small performance boost if the siblings are split such that one of the virtual partitions has no workload. If you require consistently predictable performance, configure the virtual partitions consistently; in other words, whether you split siblings or keep them together, always do the same thing.

-----------------

Hope that helps,

Duncan

[Duncan Edmonstone]

hmmm, formatting a bit screwed up there - the point is that with vparstatus -d I can see the siblings of a given CPU (siblings being cores on the same CPU module), so in the example we can see that the CPUs at HW path 0.10 and 0.11 are cores on the same CPU module.

HTH

Duncan

[techuser_1]

All good information thanks. I like that Vpars gives you this information with the command you mentioned. If you don't have vpar's installed a less eloquent way is to use cstm.

Additional information was gained here:
http://forums1.itrc.hp.com/service/forums/bizsupport/questionanswer.do?threadId=1034399

Basically if you have Support Tools installed you can use cstm.

# echo "selclass qualifier cpu;info;wait;infolog" | cstm > /tmp/cpuinfo

Look through the output file (/tmp/cpuinfo) search for Slot and notice that the Slot and serial number are the same on Dual Core Processors.

Two CPU's in the same slot... must be dual core.

Thanks both of you for responding.