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#1 2018-11-29 08:56:10

Gruntz
Member
From: Haskovo, Bulgaria
Registered: 2007-08-31
Posts: 282

Qemu, cpu pinning, numa misses.

Hello All,

I have a machine with 2 VMs on it - Windows10 (gaming) and Archlinux (working).

I want to assign 6 CPU to each system, ( 12 total ) and have 12 more spare for more VMs. (git, jenkins, testing... etc.)

For performance, I want to assign 6 cores from one CPU to Windows VM, and 6 cores from the other CPU to Archlinux VM.

I did that, but numastat shows that the only RAM in use is the one on node 0. Am I doing something wrong? Did I misunderstood the whole idea and made wrong configuration?

# My machine:
Motherboard:    Supermicro X8DTN+-F
CPU:                  2x Xeon x5650, 6 core, 2 threads ( 24 total vcpu )
RAM:                 8x8GB (4x8GB for each CPU)

No VMs running

After VMs are running:

Windows10 xml

Archlinux xml

vcpuinfo from virsh cmd

Thank you in advance.

P.S.
As I understand, I have 64GB ram, divided between the CPUs (I have physically attached 4 sticks of 8GB to the slot belonging to cpu0, and 4 sticks of 8GB to the slots belonging to cpu1. I do not use triple channel, only dual, as I was stupid and got wrong number of ram sticks). Each CPU has a direct access to its memory, but to use the other CPUs memory it has to use another path?? which makes it slower. That is why I want to pin each VM to specific CPU, so the whole VM will use only the memory from that CPU and have faster access. In future, I will pin other VMs to specific node ( cpu + its ram? ) as well, to eliminate numa misses (when one CPU uses the ram that "belongs" to the other CPU?)

Any input on the case, or remarks about the XML files are welcome, even those off-topic.

Last edited by Gruntz (2018-11-29 14:20:05)

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