[Question] Cannot sample lbr callchain on qemu-kvm guest machine

[Question] Cannot sample lbr callchain on qemu-kvm guest machine

[rainkin]

Hello~

My config:
===============
Host:
CPU: i7-10700
Kernel (5.8.0-41-generic)
Ubuntu (20.10)
Qemu (5.0.0, Debian 1:5.0-5ubuntu9.6)
===============
Guest:
CPU: host-passthrough (qemu -cpu host,migratable=on)
Kernel: 5.4.0-66-generic
Ubuntu: 18.04
perf: 5.4.86
===============

I try to collect lbr callchain on a virtual machine.
Thus I execute the following commands on the virtual machine:
"sudo perf record -e cycles --call-graph lbr"
and get the following errors:
" cycles: PMU Hardware doesn't support sampling/overflow-interrupts.
Try 'perf stat' "

Does anyone know the reason?

Thanks
Rainkin

Re: [Question] Cannot sample lbr callchain on qemu-kvm guest machine

[Ian Rogers]

On Wed, Mar 10, 2021 at 12:39 AM rainkin <rainkin1993@gmail.com> wrote:
>
> Hello~
>
> My config:
> ===============
> Host:
> CPU: i7-10700
> Kernel (5.8.0-41-generic)
> Ubuntu (20.10)
> Qemu (5.0.0, Debian 1:5.0-5ubuntu9.6)
> ===============
> Guest:
> CPU: host-passthrough (qemu -cpu host,migratable=on)
> Kernel: 5.4.0-66-generic
> Ubuntu: 18.04
> perf: 5.4.86
> ===============
>
> I try to collect lbr callchain on a virtual machine.
> Thus I execute the following commands on the virtual machine:
> "sudo perf record -e cycles --call-graph lbr"
> and get the following errors:
> " cycles: PMU Hardware doesn't support sampling/overflow-interrupts.
> Try 'perf stat' "
>
> Does anyone know the reason?

There needs to be kernel support and it looks this hasn't landed yet.
From reading:
https://lore.kernel.org/lkml/f5847034-e720-b8ce-905b-04e2cfb7661b@intel.com/

Thanks,
Ian

> Thanks
> Rainkin