linux/include/asm-i386/tsc.h
john stultz 539eb11e6e [PATCH] Time: i386 Conversion - part 2: Rework TSC Support
As part of the i386 conversion to the generic timekeeping infrastructure, this
introduces a new tsc.c file.  The code in this file replaces the TSC
initialization, management and access code currently in timer_tsc.c (which
will be removed) that we want to preserve.

The code also introduces the following functionality:

o tsc_khz: like cpu_khz but stores the TSC frequency on systems that do not
  change TSC frequency w/ CPU frequency

o check/mark_tsc_unstable: accessor/modifier flag for TSC timekeeping
  usability

o minor cleanups to calibration math.

This patch also includes a one line __cpuinitdata fix from Zwane Mwaikambo.

Signed-off-by: John Stultz <johnstul@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-06-26 09:58:21 -07:00

50 lines
1.1 KiB
C

/*
* linux/include/asm-i386/tsc.h
*
* i386 TSC related functions
*/
#ifndef _ASM_i386_TSC_H
#define _ASM_i386_TSC_H
#include <linux/config.h>
#include <asm/processor.h>
/*
* Standard way to access the cycle counter on i586+ CPUs.
* Currently only used on SMP.
*
* If you really have a SMP machine with i486 chips or older,
* compile for that, and this will just always return zero.
* That's ok, it just means that the nicer scheduling heuristics
* won't work for you.
*
* We only use the low 32 bits, and we'd simply better make sure
* that we reschedule before that wraps. Scheduling at least every
* four billion cycles just basically sounds like a good idea,
* regardless of how fast the machine is.
*/
typedef unsigned long long cycles_t;
extern unsigned int cpu_khz;
extern unsigned int tsc_khz;
static inline cycles_t get_cycles(void)
{
unsigned long long ret = 0;
#ifndef CONFIG_X86_TSC
if (!cpu_has_tsc)
return 0;
#endif
#if defined(CONFIG_X86_GENERIC) || defined(CONFIG_X86_TSC)
rdtscll(ret);
#endif
return ret;
}
extern void tsc_init(void);
extern void mark_tsc_unstable(void);
#endif