AMD Ryzen system cost more memory, cpu usage than Xeon system.

chinsu

Member
Jan 8, 2019
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Hi guys,
Im facing a problem that with the same template (Windows Server 2012R2).

Xeon host configuration: Dual E5 2695v2, Ram 128G, 1x 128G SSD, 4x 1T SSD, LVM format, No ZFS.

Ryzen host configuration: 1x Ryzen 9 3900x, Ram 128G, 1x 128G SSD, 4x 1.2T Nvme, LVM format, No ZFS.

Vm configuration:

Code:
agent: 1
balloon: 1
bootdisk: scsi0
cores: 2
cpu: kvm64
memory: 2048
name: Temp-MH
net0: virtio=AA:5F:57:BF:C7:3D,bridge=vmbr0,firewall=1,tag=1010
numa: 0
ostype: win8
scsi0: disk1:vm-999999-disk-0,size=80G
scsihw: virtio-scsi-pci
smbios1: uuid=5c0d20c3-a71a-4568-a8ac-56477da9c5d1
sockets: 1
vmgenid: caa7344c-ae0a-4bac-8d8e-785387a22af7
#qmdump#map:scsi0:drive-scsi0:disk1:raw:

When running on Xeon system, everything is working well, but when running on Ryzen one, problems appear.

On Ryzen host:
- When starting vm, memory report in vm's stats is 1.8G and only reduce after 2-3', that's strange. (On Xeon system, it's 450MB and stay constant when idle).
- Proxmox host stats show that vm cost more than 2G Ram when starting and increasing, maximum memory using after a while around 2.8G. (ex: proxmox host cost 2.5G for itself, vm cost 2.8G => total 5.3G Ram).
- When running the same number of vms with Xeon, total cpu, memory cost are higher than Xeon system alot. (Pictures below).
So is there anyone has the same problem and how to fix it?
Thank you.
 

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your load-average on ryzen seem really super high (124 with 24 cores), so it's really overloaded.

do you see some process using high cpu ? (#ps -aux ? )


root 163 60.8 0.0 0 0 ? SN Aug08 880:17 [ksmd]
root 1751 13.5 1.6 2773556 2131796 ? Sl Aug08 163:26 /usr/bin/kvm -i

they use the most cpu.
Because of high memory on vm, It has to cache more => high CPU.
But idk Why it use more memory than Xeon host.
 
Note that you are around 80% memory usage, and your ksm is already crazy high (102G ksm sharing for a 128G host is really high).

So I think balloning is in action here, to try to keep memory around 80% on host.

(by default, you should have windows vms using all their memory, until balloning is in action)

I think it really difficult to compare both systems, until you have extactly same vms with same workload.

But I really think than both systems are already at their memory limit usage capacity.
(How many vms are running on each host && how much memory is configured by vm)
 
Unusually high load always points to I/O(storage)
Xeon use sdd and Ryzen used nvme.

Note that you are around 80% memory usage, and your ksm is already crazy high (102G ksm sharing for a 128G host is really high).

So I think balloning is in action here, to try to keep memory around 80% on host.

(by default, you should have windows vms using all their memory, until balloning is in action)

I think it really difficult to compare both systems, until you have extactly same vms with same workload.

But I really think than both systems are already at their memory limit usage capacity.
(How many vms are running on each host && how much memory is configured by vm)

I use exact the same vm on both system. here is what happen when I start vm and stay idle. Vm on Ryzen use more memory than Xeon.
1597023203588.png

Task manager show nothing is using that amount of memory.
vm configuration
Code:
agent: 1
balloon: 1
bootdisk: scsi0
cores: 2
cpu: kvm64
memory: 2048

both system are running 80 Vms. Xeon handle them easily. Ryzen is much stronger than dual Xeon.
 

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I use exact the same vm on both system. here is what happen when I start vm and stay idle. Vm on Ryzen use more memory than Xeon.

looking at your windows taskmanager creenshot, you are using 80% of the memory. that's almost the value your are seeing on the ryzen screenshot.
is the task manager also display 80% memory usage in the vm on your xeon ?
 
looking at your windows taskmanager creenshot, you are using 80% of the memory. that's almost the value your are seeing on the ryzen screenshot.
is the task manager also display 80% memory usage in the vm on your xeon ?

1597044202249.png

Everything is fine on Xeon. As you can see, they are the same vm but different system.
 

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