linux-kernel - Re: [tip:perfcounters/core] perf_counter, x86: remove X86_FEATURE_ARCH

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Message-ID: <20090511100226.GA31041@elte.hu>
Date:	Mon, 11 May 2009 12:02:26 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Jaswinder Singh Rajput <jaswinder@...nel.org>
Cc:	mingo@...hat.com, hpa@...or.com, paulus@...ba.org,
	linux-kernel@...r.kernel.org, robert.richter@....com,
	a.p.zijlstra@...llo.nl, tglx@...utronix.de,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:perfcounters/core] perf_counter, x86: remove
	X86_FEATURE_ARCH_PERFMON flag for AMD cpus


* Jaswinder Singh Rajput <jaswinder@...nel.org> wrote:

> On Sun, 2009-05-10 at 08:30 +0200, Ingo Molnar wrote:
> > * Jaswinder Singh Rajput <jaswinder@...nel.org> wrote:
> > 
> > > > #define X86_FEATURE_ARCH_PERFMON (3*32+11) /* Intel Architectural PerfMon */
> > > > should be replaced by
> > > > #define X86_FEATURE_ARCH_PERFMON (3*32+11) /* Performace Monitor */
> > > > 
> > > > All x86 cpus which support performance monitor should set this feature.
> > > > 
> > > 
> > > Currently X86_FEATURE_ARCH_PERFMON is enabled for >= Intel Core2
> > > 
> > > But Performance monitor is almost supported by all Intel 
> > > processors. I am adding few MSRs list for reference to see 
> > > complete list please check arch/x86/kernel/cpu/cpu_debug.c
> > 
> > I think you are confusing two things:
> > 
> > - The 'architectural perfmon' CPU flag, enumerated in CPUID. (this 
> >   is a relatively new CPUID flag that only Intel CPUs at around 
> >   Core2 and later will report.)
> > 
> > - The concept of 'performance monitoring' - which has been present 
> >   in various x86 CPUs starting at the original Pentium (P5) 15 years 
> >   ago or so.
> > 
> > The X86_FEATURE_ARCH_PERFMON flag is for the architectural perfmon 
> > CPUID feature. If you execute CPUID you'll get that from the CPU - 
> > on Core2 and later Intel CPUs. You wont get it on AMD CPUs. You wont 
> > get it on earlier Intel CPUs.
> > 
> > And since 'Architectural Performance Monitoring' is an Intel only 
> > thing, it would not be correct to do as if AMD had the same thing. 
> > AMD has something _similar_, but not quite the same.
> > 
> 
> Thanks for clarification.
> 
> There is one more way to check performance monitor support for 
> Intel by using IA32_MISC_ENABLE MSR (0x1A0) bit 7 tells whether 
> performance monitoring is available or not.
> 
> But IA32_MISC_ENABLE MSR (0x1A0) is not available for Pentium and 
> P6.
> 
> So better I will add new cpufeature for performance monitoring for 
> x86:
> 
> X86_FEATURE_PERFMON : Performance monitor support

What is the exact wording of IA32_MISC_ENABLE bit 7 in the Intel 
documents?

	Ingo
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