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linux-next/include/asm-x86_64/tsc.h
john stultz 6bb74df481 [PATCH] clocksource init adjustments (fix bug #7426)
This patch resolves the issue found here:
http://bugme.osdl.org/show_bug.cgi?id=7426

The basic summary is:
Currently we register most of i386/x86_64 clocksources at module_init
time. Then we enable clocksource selection at late_initcall time. This
causes some problems for drivers that use gettimeofday for init
calibration routines (specifically the es1968 driver in this case),
where durring module_init, the only clocksource available is the low-res
jiffies clocksource. This may cause slight calibration errors, due to
the small sampling time used.

It should be noted that drivers that require fine grained time may not
function on architectures that do not have better then jiffies
resolution timekeeping (there are a few). However, this does not
discount the reasonable need for such fine-grained timekeeping at init
time.

Thus the solution here is to register clocksources earlier (ideally when
the hardware is being initialized), and then we enable clocksource
selection at fs_initcall (before device_initcall).

This patch should probably get some testing time in -mm, since
clocksource selection is one of the most important issues for correct
timekeeping, and I've only been able to test this on a few of my own
boxes.

Signed-off-by: John Stultz <johnstul@us.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-03-05 07:57:53 -08:00

68 lines
1.3 KiB
C

/*
* linux/include/asm-x86_64/tsc.h
*
* x86_64 TSC related functions
*/
#ifndef _ASM_x86_64_TSC_H
#define _ASM_x86_64_TSC_H
#include <asm/processor.h>
/*
* Standard way to access the cycle counter.
*/
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;
}
/* Like get_cycles, but make sure the CPU is synchronized. */
static __always_inline cycles_t get_cycles_sync(void)
{
unsigned long long ret;
#ifdef X86_FEATURE_SYNC_RDTSC
unsigned eax;
/*
* Don't do an additional sync on CPUs where we know
* RDTSC is already synchronous:
*/
alternative_io("cpuid", ASM_NOP2, X86_FEATURE_SYNC_RDTSC,
"=a" (eax), "0" (1) : "ebx","ecx","edx","memory");
#else
sync_core();
#endif
rdtscll(ret);
return ret;
}
extern void tsc_init(void);
extern void mark_tsc_unstable(void);
extern int unsynchronized_tsc(void);
extern void init_tsc_clocksource(void);
/*
* Boot-time check whether the TSCs are synchronized across
* all CPUs/cores:
*/
extern void check_tsc_sync_source(int cpu);
extern void check_tsc_sync_target(void);
#endif