Exceptions if mixing Cortex-A76 and Cortex-A55 for KVM vendor kernel 6.1.75

[eselarm]

qemu-system-aarch64 -M virt -cpu host -enable-kvm ...

only works reliably when 1 CPU core ( -smp 1). When a VM has 2 cores, it randomly worked I experienced. If virt-manager pick 2 equal cores, VM UEFI/BIOS/kernel runs OK, but if a Cortex-A76 and Cortex-A55, all sorts of exceptions are shown or just lockup 2x or 1x 100% usage.

 

In order to still be able to use KVM, start qemu-system-aarch64 as follows:

taskset --cpu-list 4-7 qemu-system-aarch64 -M virt -cpu host -enable-kvm -smp 4 ...

or

taskset --cpu-list 0-3 qemu-system-aarch64 -M virt -cpu host -enable-kvm -smp 4 ...

 

Mainline kernel 6.8.x or later does not have this problem. It can transparently use all 8 cores.

 

Userspace is Debian Bookworm based.

[eselarm]

Besides the manual CLI running of VMs with tasksel, there is also a good/acceptable way-of-working when using virt-manager/libvirt/virsh. Problem is already old I see, also the workaround here:

So in my case on a NanoPi-R6C, that I just did upgrade, so got kernels:

-rw-r--r-- 1 root root 33792512 Dec  5 18:28 vmlinuz-6.12.2-current-rockchip-rk3588
-rw-r--r-- 1 root root 39705088 Dec  1 18:38 vmlinuz-6.1.84-vendor-rk35xx

I replaced:

  <vcpu placement="static">2</vcpu>
with:
<vcpu placement='static' cpuset='2-3'>2</vcpu>
meaning now my home automation VM runs on 2x Cortex-A55 and I rebooted using the 6.1.84-vendor-rk35xx kernel. So far so good.

 

This is great as I want also to do some video transcoding HEVC->H264 in the backgound (live) and hopefully also RKNPU experiments.