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linux-next/arch/i386/kernel/tsc.c
Daniel Walker df3624aa29 [PATCH] i386: remove xtime_lock'ing around cpufreq notifier
The locking of the xtime_lock around the cpu notifier is unessesary now.
At one time the tsc was used after a frequency change for timekeeping, but
the re-write of timekeeping no longer uses the TSC unless the frequency is
constant.

The variables that are changed in this section of code had also once been
used for timekeeping, but not any longer ..

Signed-off-by: Daniel Walker <dwalker@mvista.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Cc: Andi Kleen <ak@suse.de>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: john stultz <johnstul@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2007-05-02 19:27:18 +02:00

399 lines
8.7 KiB
C

/*
* This code largely moved from arch/i386/kernel/timer/timer_tsc.c
* which was originally moved from arch/i386/kernel/time.c.
* See comments there for proper credits.
*/
#include <linux/clocksource.h>
#include <linux/workqueue.h>
#include <linux/cpufreq.h>
#include <linux/jiffies.h>
#include <linux/init.h>
#include <linux/dmi.h>
#include <asm/delay.h>
#include <asm/tsc.h>
#include <asm/io.h>
#include <asm/timer.h>
#include "mach_timer.h"
static int tsc_enabled;
/*
* On some systems the TSC frequency does not
* change with the cpu frequency. So we need
* an extra value to store the TSC freq
*/
unsigned int tsc_khz;
int tsc_disable;
#ifdef CONFIG_X86_TSC
static int __init tsc_setup(char *str)
{
printk(KERN_WARNING "notsc: Kernel compiled with CONFIG_X86_TSC, "
"cannot disable TSC.\n");
return 1;
}
#else
/*
* disable flag for tsc. Takes effect by clearing the TSC cpu flag
* in cpu/common.c
*/
static int __init tsc_setup(char *str)
{
tsc_disable = 1;
return 1;
}
#endif
__setup("notsc", tsc_setup);
/*
* code to mark and check if the TSC is unstable
* due to cpufreq or due to unsynced TSCs
*/
static int tsc_unstable;
static inline int check_tsc_unstable(void)
{
return tsc_unstable;
}
/* Accellerators for sched_clock()
* convert from cycles(64bits) => nanoseconds (64bits)
* basic equation:
* ns = cycles / (freq / ns_per_sec)
* ns = cycles * (ns_per_sec / freq)
* ns = cycles * (10^9 / (cpu_khz * 10^3))
* ns = cycles * (10^6 / cpu_khz)
*
* Then we use scaling math (suggested by george@mvista.com) to get:
* ns = cycles * (10^6 * SC / cpu_khz) / SC
* ns = cycles * cyc2ns_scale / SC
*
* And since SC is a constant power of two, we can convert the div
* into a shift.
*
* We can use khz divisor instead of mhz to keep a better percision, since
* cyc2ns_scale is limited to 10^6 * 2^10, which fits in 32 bits.
* (mathieu.desnoyers@polymtl.ca)
*
* -johnstul@us.ibm.com "math is hard, lets go shopping!"
*/
static unsigned long cyc2ns_scale __read_mostly;
#define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */
static inline void set_cyc2ns_scale(unsigned long cpu_khz)
{
cyc2ns_scale = (1000000 << CYC2NS_SCALE_FACTOR)/cpu_khz;
}
static inline unsigned long long cycles_2_ns(unsigned long long cyc)
{
return (cyc * cyc2ns_scale) >> CYC2NS_SCALE_FACTOR;
}
/*
* Scheduler clock - returns current time in nanosec units.
*/
unsigned long long sched_clock(void)
{
unsigned long long this_offset;
/*
* Fall back to jiffies if there's no TSC available:
*/
if (unlikely(!tsc_enabled))
/* No locking but a rare wrong value is not a big deal: */
return (jiffies_64 - INITIAL_JIFFIES) * (1000000000 / HZ);
/* read the Time Stamp Counter: */
get_scheduled_cycles(this_offset);
/* return the value in ns */
return cycles_2_ns(this_offset);
}
unsigned long native_calculate_cpu_khz(void)
{
unsigned long long start, end;
unsigned long count;
u64 delta64;
int i;
unsigned long flags;
local_irq_save(flags);
/* run 3 times to ensure the cache is warm */
for (i = 0; i < 3; i++) {
mach_prepare_counter();
rdtscll(start);
mach_countup(&count);
rdtscll(end);
}
/*
* Error: ECTCNEVERSET
* The CTC wasn't reliable: we got a hit on the very first read,
* or the CPU was so fast/slow that the quotient wouldn't fit in
* 32 bits..
*/
if (count <= 1)
goto err;
delta64 = end - start;
/* cpu freq too fast: */
if (delta64 > (1ULL<<32))
goto err;
/* cpu freq too slow: */
if (delta64 <= CALIBRATE_TIME_MSEC)
goto err;
delta64 += CALIBRATE_TIME_MSEC/2; /* round for do_div */
do_div(delta64,CALIBRATE_TIME_MSEC);
local_irq_restore(flags);
return (unsigned long)delta64;
err:
local_irq_restore(flags);
return 0;
}
int recalibrate_cpu_khz(void)
{
#ifndef CONFIG_SMP
unsigned long cpu_khz_old = cpu_khz;
if (cpu_has_tsc) {
cpu_khz = calculate_cpu_khz();
tsc_khz = cpu_khz;
cpu_data[0].loops_per_jiffy =
cpufreq_scale(cpu_data[0].loops_per_jiffy,
cpu_khz_old, cpu_khz);
return 0;
} else
return -ENODEV;
#else
return -ENODEV;
#endif
}
EXPORT_SYMBOL(recalibrate_cpu_khz);
#ifdef CONFIG_CPU_FREQ
/*
* if the CPU frequency is scaled, TSC-based delays will need a different
* loops_per_jiffy value to function properly.
*/
static unsigned int ref_freq = 0;
static unsigned long loops_per_jiffy_ref = 0;
static unsigned long cpu_khz_ref = 0;
static int
time_cpufreq_notifier(struct notifier_block *nb, unsigned long val, void *data)
{
struct cpufreq_freqs *freq = data;
if (!ref_freq) {
if (!freq->old){
ref_freq = freq->new;
return 0;
}
ref_freq = freq->old;
loops_per_jiffy_ref = cpu_data[freq->cpu].loops_per_jiffy;
cpu_khz_ref = cpu_khz;
}
if ((val == CPUFREQ_PRECHANGE && freq->old < freq->new) ||
(val == CPUFREQ_POSTCHANGE && freq->old > freq->new) ||
(val == CPUFREQ_RESUMECHANGE)) {
if (!(freq->flags & CPUFREQ_CONST_LOOPS))
cpu_data[freq->cpu].loops_per_jiffy =
cpufreq_scale(loops_per_jiffy_ref,
ref_freq, freq->new);
if (cpu_khz) {
if (num_online_cpus() == 1)
cpu_khz = cpufreq_scale(cpu_khz_ref,
ref_freq, freq->new);
if (!(freq->flags & CPUFREQ_CONST_LOOPS)) {
tsc_khz = cpu_khz;
set_cyc2ns_scale(cpu_khz);
/*
* TSC based sched_clock turns
* to junk w/ cpufreq
*/
mark_tsc_unstable("cpufreq changes");
}
}
}
return 0;
}
static struct notifier_block time_cpufreq_notifier_block = {
.notifier_call = time_cpufreq_notifier
};
static int __init cpufreq_tsc(void)
{
return cpufreq_register_notifier(&time_cpufreq_notifier_block,
CPUFREQ_TRANSITION_NOTIFIER);
}
core_initcall(cpufreq_tsc);
#endif
/* clock source code */
static unsigned long current_tsc_khz = 0;
static cycle_t read_tsc(void)
{
cycle_t ret;
rdtscll(ret);
return ret;
}
static struct clocksource clocksource_tsc = {
.name = "tsc",
.rating = 300,
.read = read_tsc,
.mask = CLOCKSOURCE_MASK(64),
.mult = 0, /* to be set */
.shift = 22,
.flags = CLOCK_SOURCE_IS_CONTINUOUS |
CLOCK_SOURCE_MUST_VERIFY,
};
void mark_tsc_unstable(char *reason)
{
if (!tsc_unstable) {
tsc_unstable = 1;
tsc_enabled = 0;
printk("Marking TSC unstable due to: %s.\n", reason);
/* Can be called before registration */
if (clocksource_tsc.mult)
clocksource_change_rating(&clocksource_tsc, 0);
else
clocksource_tsc.rating = 0;
}
}
EXPORT_SYMBOL_GPL(mark_tsc_unstable);
static int __init dmi_mark_tsc_unstable(struct dmi_system_id *d)
{
printk(KERN_NOTICE "%s detected: marking TSC unstable.\n",
d->ident);
tsc_unstable = 1;
return 0;
}
/* List of systems that have known TSC problems */
static struct dmi_system_id __initdata bad_tsc_dmi_table[] = {
{
.callback = dmi_mark_tsc_unstable,
.ident = "IBM Thinkpad 380XD",
.matches = {
DMI_MATCH(DMI_BOARD_VENDOR, "IBM"),
DMI_MATCH(DMI_BOARD_NAME, "2635FA0"),
},
},
{}
};
/*
* Make an educated guess if the TSC is trustworthy and synchronized
* over all CPUs.
*/
__cpuinit int unsynchronized_tsc(void)
{
if (!cpu_has_tsc || tsc_unstable)
return 1;
/*
* Intel systems are normally all synchronized.
* Exceptions must mark TSC as unstable:
*/
if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL) {
/* assume multi socket systems are not synchronized: */
if (num_possible_cpus() > 1)
tsc_unstable = 1;
}
return tsc_unstable;
}
/*
* Geode_LX - the OLPC CPU has a possibly a very reliable TSC
*/
#ifdef CONFIG_MGEODE_LX
/* RTSC counts during suspend */
#define RTSC_SUSP 0x100
static void __init check_geode_tsc_reliable(void)
{
unsigned long val;
rdmsrl(MSR_GEODE_BUSCONT_CONF0, val);
if ((val & RTSC_SUSP))
clocksource_tsc.flags &= ~CLOCK_SOURCE_MUST_VERIFY;
}
#else
static inline void check_geode_tsc_reliable(void) { }
#endif
void __init tsc_init(void)
{
if (!cpu_has_tsc || tsc_disable)
goto out_no_tsc;
cpu_khz = calculate_cpu_khz();
tsc_khz = cpu_khz;
if (!cpu_khz)
goto out_no_tsc;
printk("Detected %lu.%03lu MHz processor.\n",
(unsigned long)cpu_khz / 1000,
(unsigned long)cpu_khz % 1000);
set_cyc2ns_scale(cpu_khz);
use_tsc_delay();
/* Check and install the TSC clocksource */
dmi_check_system(bad_tsc_dmi_table);
unsynchronized_tsc();
check_geode_tsc_reliable();
current_tsc_khz = tsc_khz;
clocksource_tsc.mult = clocksource_khz2mult(current_tsc_khz,
clocksource_tsc.shift);
/* lower the rating if we already know its unstable: */
if (check_tsc_unstable()) {
clocksource_tsc.rating = 0;
clocksource_tsc.flags &= ~CLOCK_SOURCE_IS_CONTINUOUS;
} else
tsc_enabled = 1;
clocksource_register(&clocksource_tsc);
return;
out_no_tsc:
/*
* Set the tsc_disable flag if there's no TSC support, this
* makes it a fast flag for the kernel to see whether it
* should be using the TSC.
*/
tsc_disable = 1;
}