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

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Date:	Sun, 10 May 2009 12:21:50 +0530
From:	Jaswinder Singh Rajput <jaswinder@...nel.org>
To:	Ingo Molnar <mingo@...e.hu>
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

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

--
JSR



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