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Date: Thu, 17 Mar 2011 23:55:31 +1100 (EST)
From: Bruce Evans <brde@optusnet.com.au>
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To: Jung-uk Kim <jkim@FreeBSD.org>
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Cc: svn-src-head@FreeBSD.org, svn-src-all@FreeBSD.org,
	src-committers@FreeBSD.org
Subject: Re: svn commit: r219698 - head/sys/i386/include
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On Wed, 16 Mar 2011, Jung-uk Kim wrote:

> Log:
>  Rework r219679.  Always check CPU class at run-time to make it predictable.
>  Unfortunately, it pulls in <machine/cputypes.h> but it is small enough and
>  namespace pollution is minimal, I hope.
>
>  Pointed out by:	bde

Well, I don't like the namespace pollution, and the old code carefully
avoided it by using the tsc_present global.

> Modified: head/sys/i386/include/cpu.h
> ==============================================================================
> --- head/sys/i386/include/cpu.h	Wed Mar 16 12:40:58 2011	(r219697)
> +++ head/sys/i386/include/cpu.h	Wed Mar 16 16:09:08 2011	(r219698)
> @@ -39,6 +39,7 @@
> /*
>  * Definitions unique to i386 cpu support.
>  */
> +#include <machine/cputypes.h>
> #include <machine/psl.h>
> #include <machine/frame.h>
> #include <machine/segments.h>
> @@ -69,14 +70,13 @@ void	swi_vm(void *);
> static __inline uint64_t
> get_cyclecount(void)
> {
> -#if defined(I486_CPU) || defined(KLD_MODULE)
> 	struct bintime bt;
>
> -	binuptime(&bt);
> -	return ((uint64_t)bt.sec << 56 | bt.frac >> 8);
> -#else
> +	if (cpu_class == CPUCLASS_486) {
> +		binuptime(&bt);
> +		return ((uint64_t)bt.sec << 56 | bt.frac >> 8);
> +	}
> 	return (rdtsc());
> -#endif
> }
>
> #endif

cpu_class shouldn't be used for anything, and might not be able to
correctly classify whether the CPU has a TSC.  The cpu feature for
this should be used.  Using it directly with the correct includes
would give considerably more namespace pollution (md_var.h for cpu_feature
and specialreg.h for CPUID_TSC).

Although I said that tsc_present should go, it seems to be the best
thing to use here.  Rename it __cpu_feature_TSC to reflect that it is
exactly (cpu_feature & CPUID_TSC) and put underscores in its name so
as to start being even more careful about namespace pollution in cpu.h.
Or redeclare cpu_feature and CPUID_TSC.

Bruce