Re: [Qemu-devel] [PATCH V7 0/2] Add option to configure guest vPMU

[Andrew Jones <drjones@redhat.com>]

On Fri, Oct 21, 2016 at 05:53:00PM -0400, Wei Huang wrote:
> This patchset adds a pmu=[on/off] option to enable/disable vPMU support 
> for guest VM. There are several reasons to justify this option. First,
> vPMU can be problematic for cross-migration between different SoC as perf
> counters are architecture-dependent. It is more flexible to have an option
> to turn it on/off. Secondly this option matches the "pmu" option as
> supported in libvirt. To make sure backward compatible, a PMU-related
> property is added to mach-virt machine types.
> 
> The following are testing results with this patchset:
>  CONFIG (qemu-system-aarch64)                       vPMU   WARNING
>   -M virt-2.8/virt,accel=kvm -cpu host               YES    NO
>   -M virt-2.8/virt,accel=kvm -cpu host,pmu=off       NO     NO
>   -M virt-2.8/virt,accel=kvm -cpu host,pmu=on        YES    NO
>   -M virt-2.7,accel=kvm -cpu host                    YES    NO
>   -M virt-2.7,accel=kvm -cpu host,pmu=off            NO     NO
>   -M virt-2.7,accel=kvm -cpu host,pmu=on             YES    NO
>   -M virt-2.6,accel=kvm -cpu host                    NO     NO
>   -M virt-2.6,accel=kvm -cpu host,pmu=off            NO     NO
>   -M virt-2.6,accel=kvm -cpu host,pmu=on             NO     NO
> 
>   -M virt-2.8/virt,accel=tcg -cpu cortex-a57         NO     NO
>   -M virt-2.8/virt,accel=tcg -cpu cortex-a57,pmu=off NO     "No PMU property"
>   -M virt-2.8/virt,accel=tcg -cpu cortex-a57,pmu=on  NO     "No PMU property"
>   -M virt-2.7,accel=tcg -cpu cortex-a57              NO     NO
>   -M virt-2.7,accel=tcg -cpu cortex-a57,pmu=off      NO     "No PMU property"
>   -M virt-2.7,accel=tcg -cpu cortex-a57,pmu=on       NO     "No PMU property"
>   -M virt-2.6,accel=tcg -cpu cortex-a57              NO     NO
>   -M virt-2.6,accel=tcg -cpu cortex-a57,pmu=off      NO     "No PMU property"
>   -M virt-2.6,accel=tcg -cpu cortex-a57,pmu=on       NO     "No PMU property"
> 
>   -M virt-2.8/virt,accel=tcg -cpu cortex-a15         NO     NO
>   -M virt-2.8/virt,accel=tcg -cpu cortex-a15,pmu=off NO     "No PMU property"
>   -M virt-2.8/virt,accel=tcg -cpu cortex-a15,pmu=on  NO     "No PMU property"
>   -M virt-2.7,accel=tcg -cpu cortex-a15              NO     NO
>   -M virt-2.7,accel=tcg -cpu cortex-a15,pmu=off      NO     "No PMU property"
>   -M virt-2.7,accel=tcg -cpu cortex-a15,pmu=on       NO     "No PMU property"
>   -M virt-2.6,accel=tcg -cpu cortex-a15              NO     NO
>   -M virt-2.6,accel=tcg -cpu cortex-a15,pmu=off      NO     "No PMU property"
>   -M virt-2.6,accel=tcg -cpu cortex-a15,pmu=on       NO     "No PMU property"
> 
>   * "No PMU property" msg, e.g.
>     can't apply global cortex-a15-arm-cpu.pmu=off: Property '.pmu' not found
> 
> V6->V7:
>   * change has_pmu variable type from OnOffAuto to Boolean
>   * only add "pmu" property to CPU under kvm mode, default ON

Hmm, if we don't allow the property with TCG then switching a guest from
KVM to TCG will require more than just an accelerator switch. That's a
bit annoying and I think we'd have to teach it to libvirt too. I'd prefer

 -M virt-2.8,accel=tcg -cpu cortex-a57         NO     NO
 -M virt-2.8,accel=tcg -cpu cortex-a57,pmu=off NO     NO
 -M virt-2.8,accel=tcg -cpu cortex-a57,pmu=on  NO     "Warning: PMU not
yet supported with TCG" (or something)


>   * set no_pmu=true for machvirt-2.6
> 
> V5->V6:
>   * adapt patches for new machine type 2.8
> 
> V4->V5:
>   * remove comment change for has_pmu
>   * remove warning msg when pmu_default_on=TRUE && has_pmu=AUTO && tcg=TRUE
> 
> V3->V4:
>   * change has_pmu from Boolean to OnOffAuto to handle different cases
>   * "pmu" property is re-defined as DEFINE_PROP_ON_OFF_AUTO
> 
> V2->V3:
>   * revise patch 1 commit msg and if-else statement (Drew) 
>   * move property field into VirtMachineClass (Drew)
> 
> V1->V2:
>   * keep the original field name as "has_pmu"
>   * add a warning message when PMU is turned on without KVM
>   * use the feature bit to check PMU availability, instead of using has_pmu
>   * add PMU compat support to mach-virt machine type
> 
> RFC->V1:
>   * set default pmu=off
>   * change struct ARMCPU field name "has_pmu" ==> "has_host_pmu"
>   * like el3, add a new feature ARM_FEATURE_HOST_PMU
>   * "pmu" property becomes CPU dependent. Only cortex-a53/cortex-a57/host
>     running on kvm supports this option.
> 
> Thanks,
> -Wei
> 
> Wei Huang (2):
>   arm64: Add an option to turn on/off vPMU support
>   arm: virt: add PMU property to mach-virt machine type
> 
>  hw/arm/virt-acpi-build.c |  2 +-
>  hw/arm/virt.c            |  9 ++++++++-
>  target-arm/cpu.c         | 14 ++++++++++++++
>  target-arm/cpu.h         |  1 +
>  target-arm/cpu64.c       |  2 ++
>  target-arm/kvm64.c       | 17 ++++++++++++++---
>  6 files changed, 40 insertions(+), 5 deletions(-)
> 
> -- 
> 1.8.3.1
> 
>