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

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Message-ID: <2c6fcb54-482a-14dc-0fbb-58df0f9a68b5@codeaurora.org>
Date:   Thu, 2 Mar 2017 14:30:53 -0500
From:   "Leeder, Neil" <nleeder@...eaurora.org>
To:     Marc Zyngier <marc.zyngier@....com>,
        Mark Rutland <mark.rutland@....com>
Cc:     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>, nleeder@...eaurora.org
Subject: Re: [PATCH/RFC] arm64: pmu: add Qualcomm Technologies extensions

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.