Re: [Qemu-arm] [PATCH V8 0/2] Add option to configure guest vPMU

[Peter Maydell]

On 26 October 2016 at 07:28, Wei Huang <address@hidden> 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.

(Sorry, sent this as a reply to the v7 patch; resending to
attach it to the right thread...)

So what actually are we defining as "the PMU exists" here?
The PMU exists in ARMv7 and we do actually implement it
in TCG for v7 and v8 cores (though it is a minimal
architecturally-valid implementation which implements no events,
only the cycle counter).

Should the PMU registers in TCG which we currently provide on
any v7-and-better CPU be hung off ARM_FEATURE_PMU instead ?
(this would result in the behaviour of virt-2.6 for TCG
changing in that we stop providing the PMU when we did
before, but I guess that's OK.)

thanks
-- PMM