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: <CAL_JsqL2KgLQGXRLZJ3txuvytqbRRkdK1nM=5_URO2gH_nZMWw@mail.gmail.com>
Date: Tue, 20 May 2025 17:22:06 -0500
From: Rob Herring <robh@...nel.org>
To: Will Deacon <will@...nel.org>
Cc: 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>, James Clark <james.clark@...aro.org>, 
	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 Mon, May 19, 2025 at 4:59 PM Rob Herring <robh@...nel.org> 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.

I did a comparison to v18 arm_brbe.c. It was 1134 lines. I (and Mark)
have removed 332 lines and changed 369 lines. So a little more than
half remains, but the unchanged parts are a lot of 1 line helper
functions, brackets and whitespace. So given the more complex parts
have changed, I will change the authorship.

Rob