How can I further increase latency of my VM?

[Mayank006]

Memory: balloon=0
Processor: Numa=1
SCSI Controller: Virto SCSI
Machine: Default(1440fx)
Network: VirtIO

What else can I do to increase my VM latency?

 

[UdoB]

What else can I do to increase my VM latency?

To increase latency switch from KVM based virtualization to qemu64 and set "Rate limit (MB/s):" to "10" or so. This will increase overall latency massively.

If you want to decrease it: do you have multiple physical CPUs? If not --> disable Numa. (I have no idea if the effect is more than just measurable...)

That's the only hint I can derive from that small set of information you gave us.

How do you measure latency? Why do you think it is bad? What is your goal? What kind of CPU? Ram? Assigned Ram? Local Storage? NAS/SAN? Filesystem? ..., ...? Guest OS? Passthrough devices? ...?

 

[Mayank006]

To increase latency switch from KVM based virtualization to qemu64 and set "Rate limit (MB/s):" to "10" or so. This will increase overall latency massively.

If you want to decrease it: do you have multiple physical CPUs? If not --> disable Numa. (I have no idea if the effect is more than just measurable...)

That's the only hint I can derive from that small set of information you gave us.

How do you measure latency? Why do you think it is bad? What is your goal? What kind of CPU? Ram? Assigned Ram? Local Storage? NAS/SAN? Filesystem? ..., ...? Guest OS? Passthrough devices? ...?

Thanks for the reply.

We are using this VM for software that handles audio. Yes, the server has multiple physical CPUs and 32GB RAM. Does changing the KVM-based virtulization will increase the latency? and where are the Rate limit settings? It is a Debian system.

 

[UdoB]

the server has multiple physical CPUs

How many cores per CPU? If more than -let's say- eight, I would configure the VM for 1 Socket / 4 Cores and disable NUMA. Actually I am only guessing here, but managing NUMA costs some tiny bits of performance. NUMA allows to use cores of different CPUs to access the process's RAM in one single process - but I am sure it comes with a (small) price tag.

Does changing the KVM-based virtulization will increase the latency?

KVM is fine!

and where are the Rate limit settings?

An artificial limit will probably not enhance your situation. Find "<vm> --> Hardware --> Hard Disk --> "Edit" --> Bandwidth" and also "<vm> --> Hardware --> Network Device (...) - "Edit" --> Advanced [x] --> bottom half of the dialog --> Rate limit (MB/s)"

Try to answer my other questions from my post above. Just "handles audio" doesn't tell me much. But as far as I know VMs on top of a Hypervisor are not always working for realtime requirements. A guest can not be guaranteed to be able answer in a specified (small) time. And realtime audio streams may be sensitive to this - and then produce audible jitter.

This (my statement) is more guessing than knowing, sorry. I just have no virtualized realtime audio...