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

[Suzuki K Poulose]

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