linux-kernel - Re: [PATCH v2 25/31] arm64: Performance counters support

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Message-ID: <20120816105134.GJ31784@mudshark.cambridge.arm.com>
Date:	Thu, 16 Aug 2012 11:51:34 +0100
From:	Will Deacon <will.deacon@....com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Catalin Marinas <Catalin.Marinas@....com>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 25/31] arm64: Performance counters support

On Wed, Aug 15, 2012 at 04:11:11PM +0100, Arnd Bergmann wrote:
> On Tuesday 14 August 2012, Catalin Marinas wrote:
> > From: Will Deacon <will.deacon@....com>
> > 
> > This patch adds support for the AArch64 performance counters.
> > 
> > Signed-off-by: Will Deacon <will.deacon@....com>
> > Signed-off-by: Catalin Marinas <catalin.marinas@....com>
> > ---
> >  arch/arm64/include/asm/perf_event.h |   22 +
> >  arch/arm64/include/asm/pmu.h        |   82 +++
> >  arch/arm64/kernel/perf_event.c      | 1368 +++++++++++++++++++++++++++++++++++
> >  tools/perf/perf.h                   |    6 +
> 
> Can you explain how AArch64 performance counters differ from the 32
> bit ones? Do they work for AArch32 user space under AArch64 kernels?
> Is it possible to share parts of the implementation with arch/arm?

Perf should work for compat tasks, yes. I'd like to share some of the code
with arch/arm/ and I've started reworking the arch/arm/ stuff to accomodate
this better:

  git://git.kernel.org/pub/scm/linux/kernel/git/will/linux.git perf/updates

I'm not sure how well it will fit in drivers/ but I'm certainly willing to
give it a try.

Will
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