linux-kernel - Re: [PATCH 3/5] cpufreq: Add APERF/MPERF support for AMD processors

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Message-ID: <20100325110648.GA6060@aftab>
Date:	Thu, 25 Mar 2010 12:06:49 +0100
From:	Borislav Petkov <bp@...64.org>
To:	Thomas Renninger <trenn@...e.de>
Cc:	akpm@...ux-foundation.org, davej@...hat.com,
	linux@...inikbrodowski.net, mingo@...e.hu, hpa@...or.com,
	tglx@...utronix.de, cpufreq@...r.kernel.org, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/5] cpufreq: Add APERF/MPERF support for AMD processors

From: Thomas Renninger <trenn@...e.de>
Date: Thu, Mar 25, 2010 at 10:43:04AM +0100

Hi Thomas,

> On Wednesday 24 March 2010 18:46:21 Borislav Petkov wrote:
> > From: Mark Langsdorf <mark.langsdorf@....com>
> > 
> > Starting with model 10 of Family 0x10, AMD processors may have
> > support for APERF/MPERF.  Add support for identifying it and using
> > it within cpufreq.  Move the APERF/MPERF functions out of the
> > acpi-cpufreq code and into their own file so they can easily be
> > shared.
> > 
> > Signed-off-by: Mark Langsdorf <mark.langsdorf@....com>
> > Signed-off-by: Borislav Petkov <borislav.petkov@....com>
> > ---
> >  arch/x86/kernel/cpu/amd.c                  |    6 +++
> >  arch/x86/kernel/cpu/cpufreq/Makefile       |    4 +-
> >  arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c |   44 +-----------------------
> >  arch/x86/kernel/cpu/cpufreq/mperf.c        |   50 ++++++++++++++++++++++++++++
> >  arch/x86/kernel/cpu/cpufreq/mperf.h        |    9 +++++
> >  arch/x86/kernel/cpu/cpufreq/powernow-k8.c  |    8 ++++
> >  6 files changed, 77 insertions(+), 44 deletions(-)
> >  create mode 100644 arch/x86/kernel/cpu/cpufreq/mperf.c
> >  create mode 100644 arch/x86/kernel/cpu/cpufreq/mperf.h
> > 
> > diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
> > index e485825..796f662 100644
> > --- a/arch/x86/kernel/cpu/amd.c
> > +++ b/arch/x86/kernel/cpu/amd.c
> > @@ -537,6 +537,12 @@ static void __cpuinit init_amd(struct cpuinfo_x86 *c)
> >  		set_cpu_cap(c, X86_FEATURE_MFENCE_RDTSC);
> >  	}
> >  
> > +	if (c->cpuid_level >= 6) {
> > +		unsigned ecx = cpuid_ecx(6);
> > +		if (ecx & 0x01)
> > +			set_cpu_cap(c, X86_FEATURE_APERFMPERF);
> > +	}
> > +
> Can you put this into:
> arch/x86/kernel/cpu/common.c (or wherever it fits in general x86 cpu init code)
> and remove this (arch/x86/kernel/cpu/intel.c):
>         if (c->cpuid_level > 6) {
>                 unsigned ecx = cpuid_ecx(6);
>                 if (ecx & 0x01)
>                         set_cpu_cap(c, X86_FEATURE_APERFMPERF);
>         }
> 
> an x86 maintainer might want to double check, but I expect this should work
> for all x86 machines?

Yes, it should. However, there's the remote, far-fetched possibility
that other x86 vendors besides AMD and Intel, might have/plan to have
CPUID, base function 6, ECX[1] defined as a completely different feature
flag. And then it becomes ugly.

Besides, this is, strictly speaking, not x86 generic code but AMD- and
Intel-generic (huh, is there something like that? :)) code.

So, IMO, this is a judgement call based on the current settings of the
duplication and bloating levels of the x86 maintainers' filters :)

Let's have some more opinions, please...

Thanks.

-- 
Regards/Gruss,
Boris.

--
Advanced Micro Devices, Inc.
Operating Systems Research Center
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