linux-kernel - Re: [PATCH 0/2] perf: ARM CoreSight PMU support

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Date:   Wed, 11 May 2022 09:44:57 +0100
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     Will Deacon <will@...nel.org>, Sudeep Holla <sudeep.holla@....com>
Cc:     Besar Wicaksono <bwicaksono@...dia.com>, catalin.marinas@....com,
        mark.rutland@....com, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-tegra@...r.kernel.org,
        thanu.rangarajan@....com, Michael.Williams@....com,
        treding@...dia.com, jonathanh@...dia.com, vsethi@...dia.com,
        Mathieu Poirier <mathieu.poirier@...aro.org>
Subject: Re: [PATCH 0/2] perf: ARM CoreSight PMU support

On 10/05/2022 12:13, Will Deacon wrote:
> On Tue, May 10, 2022 at 12:07:42PM +0100, Sudeep Holla wrote:
>> On Mon, May 09, 2022 at 11:02:23AM +0100, Suzuki K Poulose wrote:
>>> Cc: Mike Williams, Mathieu Poirier
>>> On 09/05/2022 10:28, Will Deacon wrote:
>>>> On Sun, May 08, 2022 at 07:28:08PM -0500, Besar Wicaksono wrote:
>>>>>    arch/arm64/configs/defconfig                  |    1 +
>>>>>    drivers/perf/Kconfig                          |    2 +
>>>>>    drivers/perf/Makefile                         |    1 +
>>>>>    drivers/perf/coresight_pmu/Kconfig            |   10 +
>>>>>    drivers/perf/coresight_pmu/Makefile           |    7 +
>>>>>    .../perf/coresight_pmu/arm_coresight_pmu.c    | 1317 +++++++++++++++++
>>>>>    .../perf/coresight_pmu/arm_coresight_pmu.h    |  147 ++
>>>>>    .../coresight_pmu/arm_coresight_pmu_nvidia.c  |  300 ++++
>>>>>    .../coresight_pmu/arm_coresight_pmu_nvidia.h  |   17 +
>>>>>    9 files changed, 1802 insertions(+)
>>>>
>>>> How does this interact with all the stuff we have under
>>>> drivers/hwtracing/coresight/?
>>>
>>> Absolutely zero, except for the name. The standard
>>> is named "CoreSight PMU" which is a bit unfortunate,
>>> given the only link, AFAIU, with the "CoreSight" architecture
>>> is the Lock Access Register(LAR). For reference, the
>>> drivers/hwtracing/coresight/ is purely "CoreSight" self-hosted
>>> tracing and the PMU is called "cs_etm" (expands to coresight etm).
>>> Otherwise the standard doesn't have anything to do with what
>>> exists already in the kernel.
> 
> That's... a poor naming choice! But good, if it's entirely separate then I
> don't have to worry about that. Just wanted to make sure we're not going to
> get tangled up in things like ROM tables and Coresight power domains for
> these things.
> 
>>> One potential recommendation for the name is, "Arm PMU"  (The ACPI table is
>>> named Arm PMU Table). But then that could be clashing with the armv8_pmu
>>> :-(.
>>>
>>> Some of the other options are :
>>>
>>> "Arm Generic PMU"
>>> "Arm Uncore PMU"
>>
>> I wasn't sure on this if there is any restriction on usage of this on Arm
>> and hence didn't make the suggestion. But if allowed, this would be my
>> choice too.
> 
> We'd taken to calling them "System" PMUS in the past, so maybe just stick
> with that? I think "Uncore" is Intel terminology so it's probably best to

I thought about that, but there are some IPs named "System Profilers" 
(e.g., on Juno board) which could be easily confused. But I hope their
population in the name space is much less. So, I am happy with that
choice. The only other concern is, it doesn't indicate it supports PMUs
that are compliant to a given Arm Standard. i.e., people could think of 
this as a "single type" of PMU.
So, I am wondering if something like "Arm Standard PMU" makes any sense ?

Also, I hope the drivers would choose a name indicating the "type"  -
<vendor>_<type>_pmu (e.g., nvidia_pcie_pmu, arm_smmuv3_pmu etc) while 
registering their PMU. That way it is clearer for the PMU while the
base device could be arm_system_pmu_0 etc.

Suzuki


> avoid it for non-Intel parts.
> 
> Will