svn commit: r219698 - head/sys/i386/include

[Jung-uk Kim]

On Thursday 17 March 2011 01:02 pm, Jung-uk Kim wrote:
> On Thursday 17 March 2011 08:55 am, Bruce Evans wrote:
> > 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.
>
> Actually, I think this function must be move to machdep.c as a real
> function unless there is any serious objection.  There is no reason
> to pollute this file for awful things like this.  I know it was
> done because of performance reason in the past (such as CPU ticker,
> performance measurement, I guess.) but it is rarely used now and it
> does only one serious thing, i.e., early entropy seeding.  There is
> a minor usage in SCTP for debugging but moving it to machdep.c
> won't hurt much, I think.  What do you think?

Why can't we just use srandom(cpu_ticks()) in the first place?  I 
wonder...

Jung-uk Kim