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

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Date:   Fri, 03 Mar 2017 10:17:28 +0000
From:   Marc Zyngier <marc.zyngier@....com>
To:     "Leeder\, Neil" <nleeder@...eaurora.org>
Cc:     Mark Rutland <mark.rutland@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Mark Langsdorf <mlangsdo@...hat.com>,
        Mark Salter <msalter@...hat.com>, Jon Masters <jcm@...hat.com>,
        Timur Tabi <timur@...eaurora.org>,
        Jeremy Linton <jeremy.linton@....com>
Subject: Re: [PATCH/RFC] arm64: pmu: add Qualcomm Technologies extensions

On Thu, Mar 02 2017 at  7:30:53 pm GMT, "Leeder, Neil" <nleeder@...eaurora.org> wrote:
> 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.

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.