linux-kernel - Re: [PATCH v21 4/4] perf: arm_pmuv3: Add support for the Branch Record Buffer Extension (BRBE)

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Message-ID: <c2393238-d1cb-43bd-b67e-08105a9834fd@linaro.org>
Date: Tue, 27 May 2025 18:57:43 +0100
From: James Clark <james.clark@...aro.org>
To: Will Deacon <will@...nel.org>
Cc: Rob Herring <robh@...nel.org>, Mark Rutland <mark.rutland@....com>,
 Catalin Marinas <catalin.marinas@....com>, Jonathan Corbet <corbet@....net>,
 Marc Zyngier <maz@...nel.org>, Oliver Upton <oliver.upton@...ux.dev>,
 Joey Gouly <joey.gouly@....com>, Suzuki K Poulose <suzuki.poulose@....com>,
 Zenghui Yu <yuzenghui@...wei.com>,
 Anshuman Khandual <anshuman.khandual@....com>, Leo Yan <leo.yan@....com>,
 linux-arm-kernel@...ts.infradead.org, linux-perf-users@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
 kvmarm@...ts.linux.dev
Subject: Re: [PATCH v21 4/4] perf: arm_pmuv3: Add support for the Branch
 Record Buffer Extension (BRBE)



On 27/05/2025 11:50 am, Will Deacon wrote:
> On Wed, May 21, 2025 at 04:58:42PM +0100, James Clark wrote:
>>
>>
>> On 19/05/2025 10:56 pm, Rob Herring wrote:
>>> On Mon, May 19, 2025 at 04:06:22PM +0100, Will Deacon wrote:
>>>> Hey Rob,
>>>>
>>>> On Mon, Apr 07, 2025 at 12:41:33PM -0500, Rob Herring (Arm) wrote:
>>>>> From: Anshuman Khandual <anshuman.khandual@....com>
>>>>>
>>>>> The ARMv9.2 architecture introduces the optional Branch Record Buffer
>>>>> Extension (BRBE), which records information about branches as they are
>>>>> executed into set of branch record registers. BRBE is similar to x86's
>>>>> Last Branch Record (LBR) and PowerPC's Branch History Rolling Buffer
>>>>> (BHRB).
>>>>
>>>> Since you picked this up from v19, the driver has changed considerably
>>>> and I presume you will be continuing to extend it in future as the
>>>> architecture progresses. Perhaps having you listed as Author (and
>>>> crucially, in git blame :p) with Anshuman as a Co-developed-by: would be
>>>> more appropriate?
>>>
>>> Shrug.
>>>
>>>>> ---
>>>>>    drivers/perf/Kconfig         |  11 +
>>>>>    drivers/perf/Makefile        |   1 +
>>>>>    drivers/perf/arm_brbe.c      | 802 +++++++++++++++++++++++++++++++++++++++++++
>>>>>    drivers/perf/arm_brbe.h      |  47 +++
>>>>>    drivers/perf/arm_pmu.c       |  15 +-
>>>>>    drivers/perf/arm_pmuv3.c     | 129 ++++++-
>>>>>    include/linux/perf/arm_pmu.h |   8 +
>>>>>    7 files changed, 1006 insertions(+), 7 deletions(-)
>>>>
>>>> Do you know if James Clark's tests [1] are going to be respun for the
>>>> perf tool? It would be handy to have some way to test this new
>>>> functionality.
>>>
>>> Yes. I dropped them here because I've been told by Arnaldo in the past
>>> to send userspace stuff separately.
>>>
>>
>> That version of the test was out of date so I've pushed the new version
>> here: https://git.linaro.org/plugins/gitiles/people/james.clark/linux.git/+/16e4a18c2d5fc53736f05c9052b1d11d74909707
>>
>> But I'll wait for the driver changes to be finalised before posting it. Or
>> Rob can take it back into the patchset.
> 
> Thanks, James. I just wanted to make sure that there was still a plan
> for upstreaming these separately from the driver. Have you had a chance
> to run them against this v21?
> 
> Will


Yes I'll send it once the driver is merged. And yes they're passing 
against v21, but I'll retest v22 as well.

James