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

On Thu, Mar 02 2017 at  7:30:53 pm GMT, "Leeder, Neil" [off-list ref] wrote:

Hi Mark Z.,

On 3/2/2017 4:05 AM, Marc Zyngier wrote:

quoted

On 01/03/17 21:36, Leeder, Neil wrote:

quoted

On 3/1/2017 1:10 PM, Mark Rutland wrote:

quoted

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.

How do you know that? I'm afraid this is not something you or I can
guarantee (and even less enforce).

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?

At the moment, it seems that there is a consensus against adding support
for an IMPDEF PMU.

Thanks,

	M.
-- 
Jazz is not dead, it just smell funny.