Re: [PATCH/RFC] arm64: pmu: add Qualcomm Technologies extensions

Leeder, Neil
2017-03-02T19:31:06Z

Hi Mark Z.,

On 3/2/2017 4:05 AM, Marc Zyngier wrote:
> On 01/03/17 21:36, Leeder, Neil wrote:
>> On 3/1/2017 1:10 PM, Mark Rutland wrote:
>>> KVM already has (architected) PMU support, and without a corresponding
>>> KVM patch this is at best insufficient. I don't imagine the KVM folk
>>> will be too thrilled about the prospect of emulating an IMPLEMENTATION
>>> DEFINED CPU feature like this.
>>
>> Does KVM handle ARMv7 PMU implementations? If so, do you know what it
>> does for the scorpion_* and krait_* implementations in
>> arch/arm/kernel/perf_events_v7.c? These extensions in ARMv8 are very
>> similar to the krait extensions, with some 64-bit tweaks, so could be
>> handled by KVM the same way it handles the ARMv7 cases.
>
> No, KVM doesn't handle the ARMv7 PMU at all. I'm not aware of the
> virtualization extensions being available on Scorpion or Krait, which
> makes it a moot point. What it handles is the PMUv3 architecture.

Thank you for the explanation.

This driver is specifically for Qualcomm Technologies server chips. They
will not be in a heterogenous environment with non-Qualcomm processors,
so there should be no migration issues.

If we were to provide a patch which added KVM support for the 4
additional registers here, would you consider reviewing it, or is adding
implementation-defined registers a show-stopper?

Thanks,
Neil
--
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm
Technologies Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project.