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SubjectRe: [PATCH 3/5] cpufreq: Add APERF/MPERF support for AMD processors
From: Thomas Renninger <trenn@suse.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@amd.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@amd.com>
> > Signed-off-by: Borislav Petkov <borislav.petkov@amd.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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