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Commit e8498001 authored by John Stultz's avatar John Stultz Committed by David S. Miller
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[PATCH] linux-2.5.41_timer-changes_A4 (2/3 - bulk move) 

        This is part 2 of 3 of my timer-change patch. Part 2 is just a
bulk move of code out of time.c and into timer_pit.c and timer_tsc.c. No
code is changed, only moved.

        Please note, this code will not compile without the final third
part of this patch collection. This was done for readability alone.
parent c710b958
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Showing with 359 additions and 351 deletions
arch/i386/kernel/time.c
View file @ e8498001
...@@ -73,51 +73,11 @@ u64 jiffies_64; ...@@ -73,51 +73,11 @@ u64 jiffies_64;
unsigned long cpu_khz; /* Detected as we calibrate the TSC */ unsigned long cpu_khz; /* Detected as we calibrate the TSC */
/* Number of usecs that the last interrupt was delayed */
static int delay_at_last_interrupt;
static unsigned long last_tsc_low; /* lsb 32 bits of Time Stamp Counter */
/* Cached *multiplier* to convert TSC counts to microseconds.
* (see the equation below).
* Equal to 2^32 * (1 / (clocks per usec) ).
* Initialized in time_init.
*/
unsigned long fast_gettimeoffset_quotient;
extern rwlock_t xtime_lock; extern rwlock_t xtime_lock;
extern unsigned long wall_jiffies; extern unsigned long wall_jiffies;
spinlock_t rtc_lock = SPIN_LOCK_UNLOCKED; spinlock_t rtc_lock = SPIN_LOCK_UNLOCKED;
static inline unsigned long do_fast_gettimeoffset(void)
{
register unsigned long eax, edx;
/* Read the Time Stamp Counter */
rdtsc(eax,edx);
/* .. relative to previous jiffy (32 bits is enough) */
eax -= last_tsc_low; /* tsc_low delta */
/*
* Time offset = (tsc_low delta) * fast_gettimeoffset_quotient
* = (tsc_low delta) * (usecs_per_clock)
* = (tsc_low delta) * (usecs_per_jiffy / clocks_per_jiffy)
*
* Using a mull instead of a divl saves up to 31 clock cycles
* in the critical path.
*/
__asm__("mull %2"
:"=a" (eax), "=d" (edx)
:"rm" (fast_gettimeoffset_quotient),
"0" (eax));
/* our adjusted time offset in microseconds */
return delay_at_last_interrupt + edx;
}
#define TICK_SIZE (tick_nsec / 1000) #define TICK_SIZE (tick_nsec / 1000)
...@@ -125,104 +85,6 @@ spinlock_t i8253_lock = SPIN_LOCK_UNLOCKED; ...@@ -125,104 +85,6 @@ spinlock_t i8253_lock = SPIN_LOCK_UNLOCKED;
EXPORT_SYMBOL(i8253_lock); EXPORT_SYMBOL(i8253_lock);
#ifndef CONFIG_X86_TSC #ifndef CONFIG_X86_TSC
/* This function must be called with interrupts disabled
* It was inspired by Steve McCanne's microtime-i386 for BSD. -- jrs
*
* However, the pc-audio speaker driver changes the divisor so that
* it gets interrupted rather more often - it loads 64 into the
* counter rather than 11932! This has an adverse impact on
* do_gettimeoffset() -- it stops working! What is also not
* good is that the interval that our timer function gets called
* is no longer 10.0002 ms, but 9.9767 ms. To get around this
* would require using a different timing source. Maybe someone
* could use the RTC - I know that this can interrupt at frequencies
* ranging from 8192Hz to 2Hz. If I had the energy, I'd somehow fix
* it so that at startup, the timer code in sched.c would select
* using either the RTC or the 8253 timer. The decision would be
* based on whether there was any other device around that needed
* to trample on the 8253. I'd set up the RTC to interrupt at 1024 Hz,
* and then do some jiggery to have a version of do_timer that
* advanced the clock by 1/1024 s. Every time that reached over 1/100
* of a second, then do all the old code. If the time was kept correct
* then do_gettimeoffset could just return 0 - there is no low order
* divider that can be accessed.
*
* Ideally, you would be able to use the RTC for the speaker driver,
* but it appears that the speaker driver really needs interrupt more
* often than every 120 us or so.
*
* Anyway, this needs more thought.... pjsg (1993-08-28)
*
* If you are really that interested, you should be reading
* comp.protocols.time.ntp!
*/
static unsigned long do_slow_gettimeoffset(void)
{
int count;
static int count_p = LATCH; /* for the first call after boot */
static unsigned long jiffies_p = 0;
/*
* cache volatile jiffies temporarily; we have IRQs turned off.
*/
unsigned long jiffies_t;
/* gets recalled with irq locally disabled */
spin_lock(&i8253_lock);
/* timer count may underflow right here */
outb_p(0x00, 0x43); /* latch the count ASAP */
count = inb_p(0x40); /* read the latched count */
/*
* We do this guaranteed double memory access instead of a _p
* postfix in the previous port access. Wheee, hackady hack
*/
jiffies_t = jiffies;
count |= inb_p(0x40) << 8;
/* VIA686a test code... reset the latch if count > max + 1 */
if (count > LATCH) {
outb_p(0x34, 0x43);
outb_p(LATCH & 0xff, 0x40);
outb(LATCH >> 8, 0x40);
count = LATCH - 1;
}
spin_unlock(&i8253_lock);
/*
* avoiding timer inconsistencies (they are rare, but they happen)...
* there are two kinds of problems that must be avoided here:
* 1. the timer counter underflows
* 2. hardware problem with the timer, not giving us continuous time,
* the counter does small "jumps" upwards on some Pentium systems,
* (see c't 95/10 page 335 for Neptun bug.)
*/
if( jiffies_t == jiffies_p ) {
if( count > count_p ) {
/* the nutcase */
count = do_timer_overflow(count);
}
} else
jiffies_p = jiffies_t;
count_p = count;
count = ((LATCH-1) - count) * TICK_SIZE;
count = (count + LATCH/2) / LATCH;
return count;
}
static unsigned long (*do_gettimeoffset)(void) = do_slow_gettimeoffset;
#else #else
#define do_gettimeoffset() do_fast_gettimeoffset() #define do_gettimeoffset() do_fast_gettimeoffset()
...@@ -433,34 +295,7 @@ void timer_interrupt(int irq, void *dev_id, struct pt_regs *regs) ...@@ -433,34 +295,7 @@ void timer_interrupt(int irq, void *dev_id, struct pt_regs *regs)
*/ */
write_lock(&xtime_lock); write_lock(&xtime_lock);
if (use_tsc)
{
/*
* It is important that these two operations happen almost at
* the same time. We do the RDTSC stuff first, since it's
* faster. To avoid any inconsistencies, we need interrupts
* disabled locally.
*/
/*
* Interrupts are just disabled locally since the timer irq
* has the SA_INTERRUPT flag set. -arca
*/
/* read Pentium cycle counter */
rdtscl(last_tsc_low);
spin_lock(&i8253_lock);
outb_p(0x00, 0x43); /* latch the count ASAP */
count = inb_p(0x40); /* read the latched count */
count |= inb(0x40) << 8;
spin_unlock(&i8253_lock);
count = ((LATCH-1) - count) * TICK_SIZE;
delay_at_last_interrupt = (count + LATCH/2) / LATCH;
}
do_timer_interrupt(irq, NULL, regs); do_timer_interrupt(irq, NULL, regs);
...@@ -510,85 +345,6 @@ unsigned long get_cmos_time(void) ...@@ -510,85 +345,6 @@ unsigned long get_cmos_time(void)
return mktime(year, mon, day, hour, min, sec); return mktime(year, mon, day, hour, min, sec);
} }
/* ------ Calibrate the TSC -------
* Return 2^32 * (1 / (TSC clocks per usec)) for do_fast_gettimeoffset().
* Too much 64-bit arithmetic here to do this cleanly in C, and for
* accuracy's sake we want to keep the overhead on the CTC speaker (channel 2)
* output busy loop as low as possible. We avoid reading the CTC registers
* directly because of the awkward 8-bit access mechanism of the 82C54
* device.
*/
#define CALIBRATE_LATCH (5 * LATCH)
#define CALIBRATE_TIME (5 * 1000020/HZ)
#ifdef CONFIG_X86_TSC
static unsigned long __init calibrate_tsc(void)
{
/* Set the Gate high, disable speaker */
outb((inb(0x61) & ~0x02) | 0x01, 0x61);
/*
* Now let's take care of CTC channel 2
*
* Set the Gate high, program CTC channel 2 for mode 0,
* (interrupt on terminal count mode), binary count,
* load 5 * LATCH count, (LSB and MSB) to begin countdown.
*/
outb(0xb0, 0x43); /* binary, mode 0, LSB/MSB, Ch 2 */
outb(CALIBRATE_LATCH & 0xff, 0x42); /* LSB of count */
outb(CALIBRATE_LATCH >> 8, 0x42); /* MSB of count */
{
unsigned long startlow, starthigh;
unsigned long endlow, endhigh;
unsigned long count;
rdtsc(startlow,starthigh);
count = 0;
do {
count++;
} while ((inb(0x61) & 0x20) == 0);
rdtsc(endlow,endhigh);
last_tsc_low = endlow;
/* Error: ECTCNEVERSET */
if (count <= 1)
goto bad_ctc;
/* 64-bit subtract - gcc just messes up with long longs */
__asm__("subl %2,%0\n\t"
"sbbl %3,%1"
:"=a" (endlow), "=d" (endhigh)
:"g" (startlow), "g" (starthigh),
"0" (endlow), "1" (endhigh));
/* Error: ECPUTOOFAST */
if (endhigh)
goto bad_ctc;
/* Error: ECPUTOOSLOW */
if (endlow <= CALIBRATE_TIME)
goto bad_ctc;
__asm__("divl %2"
:"=a" (endlow), "=d" (endhigh)
:"r" (endlow), "0" (0), "1" (CALIBRATE_TIME));
return endlow;
}
/*
* 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..
*/
bad_ctc:
return 0;
}
#endif /* CONFIG_X86_TSC */
static struct sys_device device_i8253 = { static struct sys_device device_i8253 = {
.name = "rtc", .name = "rtc",
.id = 0, .id = 0,
...@@ -605,119 +361,12 @@ static int time_init_device(void) ...@@ -605,119 +361,12 @@ static int time_init_device(void)
device_initcall(time_init_device); device_initcall(time_init_device);
#ifdef CONFIG_CPU_FREQ
static int
time_cpufreq_notifier(struct notifier_block *nb, unsigned long val,
void *data)
{
struct cpufreq_freqs *freq = data;
unsigned int i;
if (!cpu_has_tsc)
return 0;
switch (val) {
case CPUFREQ_PRECHANGE:
if ((freq->old < freq->new) &&
((freq->cpu == CPUFREQ_ALL_CPUS) || (freq->cpu == 0))) {
cpu_khz = cpufreq_scale(cpu_khz, freq->old, freq->new);
fast_gettimeoffset_quotient = cpufreq_scale(fast_gettimeoffset_quotient, freq->new, freq->old);
}
for (i=0; i<NR_CPUS; i++)
if ((freq->cpu == CPUFREQ_ALL_CPUS) || (freq->cpu == i))
cpu_data[i].loops_per_jiffy = cpufreq_scale(cpu_data[i].loops_per_jiffy, freq->old, freq->new);
break;
case CPUFREQ_POSTCHANGE:
if ((freq->new < freq->old) &&
((freq->cpu == CPUFREQ_ALL_CPUS) || (freq->cpu == 0))) {
cpu_khz = cpufreq_scale(cpu_khz, freq->old, freq->new);
fast_gettimeoffset_quotient = cpufreq_scale(fast_gettimeoffset_quotient, freq->new, freq->old);
}
for (i=0; i<NR_CPUS; i++)
if ((freq->cpu == CPUFREQ_ALL_CPUS) || (freq->cpu == i))
cpu_data[i].loops_per_jiffy = cpufreq_scale(cpu_data[i].loops_per_jiffy, freq->old, freq->new);
break;
}
return 0;
}
static struct notifier_block time_cpufreq_notifier_block = {
notifier_call: time_cpufreq_notifier
};
#endif
void __init time_init(void) void __init time_init(void)
{ {
#ifdef CONFIG_X86_TSC
extern int x86_udelay_tsc;
#endif
xtime.tv_sec = get_cmos_time(); xtime.tv_sec = get_cmos_time();
xtime.tv_nsec = 0; xtime.tv_nsec = 0;
/*
* If we have APM enabled or the CPU clock speed is variable
* (CPU stops clock on HLT or slows clock to save power)
* then the TSC timestamps may diverge by up to 1 jiffy from
* 'real time' but nothing will break.
* The most frequent case is that the CPU is "woken" from a halt
* state by the timer interrupt itself, so we get 0 error. In the
* rare cases where a driver would "wake" the CPU and request a
* timestamp, the maximum error is < 1 jiffy. But timestamps are
* still perfectly ordered.
* Note that the TSC counter will be reset if APM suspends
* to disk; this won't break the kernel, though, 'cuz we're
* smart. See arch/i386/kernel/apm.c.
*/
#ifdef CONFIG_X86_TSC
/*
* Firstly we have to do a CPU check for chips with
* a potentially buggy TSC. At this point we haven't run
* the ident/bugs checks so we must run this hook as it
* may turn off the TSC flag.
*
* NOTE: this doesnt yet handle SMP 486 machines where only
* some CPU's have a TSC. Thats never worked and nobody has
* moaned if you have the only one in the world - you fix it!
*/
dodgy_tsc();
if (cpu_has_tsc) {
unsigned long tsc_quotient = calibrate_tsc();
if (tsc_quotient) {
fast_gettimeoffset_quotient = tsc_quotient;
use_tsc = 1;
/*
* We could be more selective here I suspect
* and just enable this for the next intel chips ?
*/
x86_udelay_tsc = 1;
#ifndef do_gettimeoffset
do_gettimeoffset = do_fast_gettimeoffset;
#endif
/* report CPU clock rate in Hz.
* The formula is (10^6 * 2^32) / (2^32 * 1 / (clocks/us)) =
* clock/second. Our precision is about 100 ppm.
*/
{ unsigned long eax=0, edx=1000;
__asm__("divl %2"
:"=a" (cpu_khz), "=d" (edx)
:"r" (tsc_quotient),
"0" (eax), "1" (edx));
printk("Detected %lu.%03lu MHz processor.\n", cpu_khz / 1000, cpu_khz % 1000);
}
#ifdef CONFIG_CPU_FREQ
cpufreq_register_notifier(&time_cpufreq_notifier_block, CPUFREQ_TRANSITION_NOTIFIER);
#endif
}
}
#endif /* CONFIG_X86_TSC */
time_init_hook(); time_init_hook();
} }
arch/i386/kernel/timers/timer_pit.c 0 → 100644
View file @ e8498001
/* This function must be called with interrupts disabled
* It was inspired by Steve McCanne's microtime-i386 for BSD. -- jrs
*
* However, the pc-audio speaker driver changes the divisor so that
* it gets interrupted rather more often - it loads 64 into the
* counter rather than 11932! This has an adverse impact on
* do_gettimeoffset() -- it stops working! What is also not
* good is that the interval that our timer function gets called
* is no longer 10.0002 ms, but 9.9767 ms. To get around this
* would require using a different timing source. Maybe someone
* could use the RTC - I know that this can interrupt at frequencies
* ranging from 8192Hz to 2Hz. If I had the energy, I'd somehow fix
* it so that at startup, the timer code in sched.c would select
* using either the RTC or the 8253 timer. The decision would be
* based on whether there was any other device around that needed
* to trample on the 8253. I'd set up the RTC to interrupt at 1024 Hz,
* and then do some jiggery to have a version of do_timer that
* advanced the clock by 1/1024 s. Every time that reached over 1/100
* of a second, then do all the old code. If the time was kept correct
* then do_gettimeoffset could just return 0 - there is no low order
* divider that can be accessed.
*
* Ideally, you would be able to use the RTC for the speaker driver,
* but it appears that the speaker driver really needs interrupt more
* often than every 120 us or so.
*
* Anyway, this needs more thought.... pjsg (1993-08-28)
*
* If you are really that interested, you should be reading
* comp.protocols.time.ntp!
*/
static unsigned long do_slow_gettimeoffset(void)
{
int count;
static int count_p = LATCH; /* for the first call after boot */
static unsigned long jiffies_p = 0;
/*
* cache volatile jiffies temporarily; we have IRQs turned off.
*/
unsigned long jiffies_t;
/* gets recalled with irq locally disabled */
spin_lock(&i8253_lock);
/* timer count may underflow right here */
outb_p(0x00, 0x43); /* latch the count ASAP */
count = inb_p(0x40); /* read the latched count */
/*
* We do this guaranteed double memory access instead of a _p
* postfix in the previous port access. Wheee, hackady hack
*/
jiffies_t = jiffies;
count |= inb_p(0x40) << 8;
/* VIA686a test code... reset the latch if count > max + 1 */
if (count > LATCH) {
outb_p(0x34, 0x43);
outb_p(LATCH & 0xff, 0x40);
outb(LATCH >> 8, 0x40);
count = LATCH - 1;
}
spin_unlock(&i8253_lock);
/*
* avoiding timer inconsistencies (they are rare, but they happen)...
* there are two kinds of problems that must be avoided here:
* 1. the timer counter underflows
* 2. hardware problem with the timer, not giving us continuous time,
* the counter does small "jumps" upwards on some Pentium systems,
* (see c't 95/10 page 335 for Neptun bug.)
*/
if( jiffies_t == jiffies_p ) {
if( count > count_p ) {
/* the nutcase */
count = do_timer_overflow(count);
}
} else
jiffies_p = jiffies_t;
count_p = count;
count = ((LATCH-1) - count) * TICK_SIZE;
count = (count + LATCH/2) / LATCH;
return count;
}
static unsigned long (*do_gettimeoffset)(void) = do_slow_gettimeoffset;
arch/i386/kernel/timers/timer_tsc.c 0 → 100644
View file @ e8498001
/* Number of usecs that the last interrupt was delayed */
static int delay_at_last_interrupt;
static unsigned long last_tsc_low; /* lsb 32 bits of Time Stamp Counter */
/* Cached *multiplier* to convert TSC counts to microseconds.
* (see the equation below).
* Equal to 2^32 * (1 / (clocks per usec) ).
* Initialized in time_init.
*/
unsigned long fast_gettimeoffset_quotient;
static inline unsigned long do_fast_gettimeoffset(void)
{
register unsigned long eax, edx;
/* Read the Time Stamp Counter */
rdtsc(eax,edx);
/* .. relative to previous jiffy (32 bits is enough) */
eax -= last_tsc_low; /* tsc_low delta */
/*
* Time offset = (tsc_low delta) * fast_gettimeoffset_quotient
* = (tsc_low delta) * (usecs_per_clock)
* = (tsc_low delta) * (usecs_per_jiffy / clocks_per_jiffy)
*
* Using a mull instead of a divl saves up to 31 clock cycles
* in the critical path.
*/
__asm__("mull %2"
:"=a" (eax), "=d" (edx)
:"rm" (fast_gettimeoffset_quotient),
"0" (eax));
/* our adjusted time offset in microseconds */
return delay_at_last_interrupt + edx;
}
if (use_tsc)
{
/*
* It is important that these two operations happen almost at
* the same time. We do the RDTSC stuff first, since it's
* faster. To avoid any inconsistencies, we need interrupts
* disabled locally.
*/
/*
* Interrupts are just disabled locally since the timer irq
* has the SA_INTERRUPT flag set. -arca
*/
/* read Pentium cycle counter */
rdtscl(last_tsc_low);
spin_lock(&i8253_lock);
outb_p(0x00, 0x43); /* latch the count ASAP */
count = inb_p(0x40); /* read the latched count */
count |= inb(0x40) << 8;
spin_unlock(&i8253_lock);
count = ((LATCH-1) - count) * TICK_SIZE;
delay_at_last_interrupt = (count + LATCH/2) / LATCH;
}
/* ------ Calibrate the TSC -------
* Return 2^32 * (1 / (TSC clocks per usec)) for do_fast_gettimeoffset().
* Too much 64-bit arithmetic here to do this cleanly in C, and for
* accuracy's sake we want to keep the overhead on the CTC speaker (channel 2)
* output busy loop as low as possible. We avoid reading the CTC registers
* directly because of the awkward 8-bit access mechanism of the 82C54
* device.
*/
#define CALIBRATE_LATCH (5 * LATCH)
#define CALIBRATE_TIME (5 * 1000020/HZ)
#ifdef CONFIG_X86_TSC
static unsigned long __init calibrate_tsc(void)
{
/* Set the Gate high, disable speaker */
outb((inb(0x61) & ~0x02) | 0x01, 0x61);
/*
* Now let's take care of CTC channel 2
*
* Set the Gate high, program CTC channel 2 for mode 0,
* (interrupt on terminal count mode), binary count,
* load 5 * LATCH count, (LSB and MSB) to begin countdown.
*/
outb(0xb0, 0x43); /* binary, mode 0, LSB/MSB, Ch 2 */
outb(CALIBRATE_LATCH & 0xff, 0x42); /* LSB of count */
outb(CALIBRATE_LATCH >> 8, 0x42); /* MSB of count */
{
unsigned long startlow, starthigh;
unsigned long endlow, endhigh;
unsigned long count;
rdtsc(startlow,starthigh);
count = 0;
do {
count++;
} while ((inb(0x61) & 0x20) == 0);
rdtsc(endlow,endhigh);
last_tsc_low = endlow;
/* Error: ECTCNEVERSET */
if (count <= 1)
goto bad_ctc;
/* 64-bit subtract - gcc just messes up with long longs */
__asm__("subl %2,%0\n\t"
"sbbl %3,%1"
:"=a" (endlow), "=d" (endhigh)
:"g" (startlow), "g" (starthigh),
"0" (endlow), "1" (endhigh));
/* Error: ECPUTOOFAST */
if (endhigh)
goto bad_ctc;
/* Error: ECPUTOOSLOW */
if (endlow <= CALIBRATE_TIME)
goto bad_ctc;
__asm__("divl %2"
:"=a" (endlow), "=d" (endhigh)
:"r" (endlow), "0" (0), "1" (CALIBRATE_TIME));
return endlow;
}
/*
* 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..
*/
bad_ctc:
return 0;
}
#endif /* CONFIG_X86_TSC */
#ifdef CONFIG_CPU_FREQ
static int
time_cpufreq_notifier(struct notifier_block *nb, unsigned long val,
void *data)
{
struct cpufreq_freqs *freq = data;
unsigned int i;
if (!cpu_has_tsc)
return 0;
switch (val) {
case CPUFREQ_PRECHANGE:
if ((freq->old < freq->new) &&
((freq->cpu == CPUFREQ_ALL_CPUS) || (freq->cpu == 0))) {
cpu_khz = cpufreq_scale(cpu_khz, freq->old, freq->new);
fast_gettimeoffset_quotient = cpufreq_scale(fast_gettimeoffset_quotient, freq->new, freq->old);
}
for (i=0; i<NR_CPUS; i++)
if ((freq->cpu == CPUFREQ_ALL_CPUS) || (freq->cpu == i))
cpu_data[i].loops_per_jiffy = cpufreq_scale(cpu_data[i].loops_per_jiffy, freq->old, freq->new);
break;
case CPUFREQ_POSTCHANGE:
if ((freq->new < freq->old) &&
((freq->cpu == CPUFREQ_ALL_CPUS) || (freq->cpu == 0))) {
cpu_khz = cpufreq_scale(cpu_khz, freq->old, freq->new);
fast_gettimeoffset_quotient = cpufreq_scale(fast_gettimeoffset_quotient, freq->new, freq->old);
}
for (i=0; i<NR_CPUS; i++)
if ((freq->cpu == CPUFREQ_ALL_CPUS) || (freq->cpu == i))
cpu_data[i].loops_per_jiffy = cpufreq_scale(cpu_data[i].loops_per_jiffy, freq->old, freq->new);
break;
}
return 0;
}
static struct notifier_block time_cpufreq_notifier_block = {
notifier_call: time_cpufreq_notifier
};
#endif
#ifdef CONFIG_X86_TSC
extern int x86_udelay_tsc;
#endif
/*
* If we have APM enabled or the CPU clock speed is variable
* (CPU stops clock on HLT or slows clock to save power)
* then the TSC timestamps may diverge by up to 1 jiffy from
* 'real time' but nothing will break.
* The most frequent case is that the CPU is "woken" from a halt
* state by the timer interrupt itself, so we get 0 error. In the
* rare cases where a driver would "wake" the CPU and request a
* timestamp, the maximum error is < 1 jiffy. But timestamps are
* still perfectly ordered.
* Note that the TSC counter will be reset if APM suspends
* to disk; this won't break the kernel, though, 'cuz we're
* smart. See arch/i386/kernel/apm.c.
*/
#ifdef CONFIG_X86_TSC
/*
* Firstly we have to do a CPU check for chips with
* a potentially buggy TSC. At this point we haven't run
* the ident/bugs checks so we must run this hook as it
* may turn off the TSC flag.
*
* NOTE: this doesnt yet handle SMP 486 machines where only
* some CPU's have a TSC. Thats never worked and nobody has
* moaned if you have the only one in the world - you fix it!
*/
dodgy_tsc();
if (cpu_has_tsc) {
unsigned long tsc_quotient = calibrate_tsc();
if (tsc_quotient) {
fast_gettimeoffset_quotient = tsc_quotient;
use_tsc = 1;
/*
* We could be more selective here I suspect
* and just enable this for the next intel chips ?
*/
x86_udelay_tsc = 1;
#ifndef do_gettimeoffset
do_gettimeoffset = do_fast_gettimeoffset;
#endif
/* report CPU clock rate in Hz.
* The formula is (10^6 * 2^32) / (2^32 * 1 / (clocks/us)) =
* clock/second. Our precision is about 100 ppm.
*/
{ unsigned long eax=0, edx=1000;
__asm__("divl %2"
:"=a" (cpu_khz), "=d" (edx)
:"r" (tsc_quotient),
"0" (eax), "1" (edx));
printk("Detected %lu.%03lu MHz processor.\n", cpu_khz / 1000, cpu_khz % 1000);
}
#ifdef CONFIG_CPU_FREQ
cpufreq_register_notifier(&time_cpufreq_notifier_block, CPUFREQ_TRANSITION_NOTIFIER);
#endif
}
}
#endif /* CONFIG_X86_TSC */
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