aboutsummaryrefslogtreecommitdiff
path: root/arch/x86/kernel/tsc.c
diff options
context:
space:
mode:
Diffstat (limited to 'arch/x86/kernel/tsc.c')
-rw-r--r--arch/x86/kernel/tsc.c302
1 files changed, 238 insertions, 64 deletions
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 8f98e9de1b8..424093b157d 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -55,7 +55,7 @@ u64 native_sched_clock(void)
rdtscll(this_offset);
/* return the value in ns */
- return cycles_2_ns(this_offset);
+ return __cycles_2_ns(this_offset);
}
/* We need to define a real function for sched_clock, to override the
@@ -104,7 +104,7 @@ __setup("notsc", notsc_setup);
/*
* Read TSC and the reference counters. Take care of SMI disturbance
*/
-static u64 tsc_read_refs(u64 *pm, u64 *hpet)
+static u64 tsc_read_refs(u64 *p, int hpet)
{
u64 t1, t2;
int i;
@@ -112,9 +112,9 @@ static u64 tsc_read_refs(u64 *pm, u64 *hpet)
for (i = 0; i < MAX_RETRIES; i++) {
t1 = get_cycles();
if (hpet)
- *hpet = hpet_readl(HPET_COUNTER) & 0xFFFFFFFF;
+ *p = hpet_readl(HPET_COUNTER) & 0xFFFFFFFF;
else
- *pm = acpi_pm_read_early();
+ *p = acpi_pm_read_early();
t2 = get_cycles();
if ((t2 - t1) < SMI_TRESHOLD)
return t2;
@@ -123,13 +123,59 @@ static u64 tsc_read_refs(u64 *pm, u64 *hpet)
}
/*
+ * Calculate the TSC frequency from HPET reference
+ */
+static unsigned long calc_hpet_ref(u64 deltatsc, u64 hpet1, u64 hpet2)
+{
+ u64 tmp;
+
+ if (hpet2 < hpet1)
+ hpet2 += 0x100000000ULL;
+ hpet2 -= hpet1;
+ tmp = ((u64)hpet2 * hpet_readl(HPET_PERIOD));
+ do_div(tmp, 1000000);
+ do_div(deltatsc, tmp);
+
+ return (unsigned long) deltatsc;
+}
+
+/*
+ * Calculate the TSC frequency from PMTimer reference
+ */
+static unsigned long calc_pmtimer_ref(u64 deltatsc, u64 pm1, u64 pm2)
+{
+ u64 tmp;
+
+ if (!pm1 && !pm2)
+ return ULONG_MAX;
+
+ if (pm2 < pm1)
+ pm2 += (u64)ACPI_PM_OVRRUN;
+ pm2 -= pm1;
+ tmp = pm2 * 1000000000LL;
+ do_div(tmp, PMTMR_TICKS_PER_SEC);
+ do_div(deltatsc, tmp);
+
+ return (unsigned long) deltatsc;
+}
+
+#define CAL_MS 10
+#define CAL_LATCH (CLOCK_TICK_RATE / (1000 / CAL_MS))
+#define CAL_PIT_LOOPS 1000
+
+#define CAL2_MS 50
+#define CAL2_LATCH (CLOCK_TICK_RATE / (1000 / CAL2_MS))
+#define CAL2_PIT_LOOPS 5000
+
+
+/*
* Try to calibrate the TSC against the Programmable
* Interrupt Timer and return the frequency of the TSC
* in kHz.
*
* Return ULONG_MAX on failure to calibrate.
*/
-static unsigned long pit_calibrate_tsc(void)
+static unsigned long pit_calibrate_tsc(u32 latch, unsigned long ms, int loopmin)
{
u64 tsc, t1, t2, delta;
unsigned long tscmin, tscmax;
@@ -144,8 +190,8 @@ static unsigned long pit_calibrate_tsc(void)
* (LSB then MSB) to begin countdown.
*/
outb(0xb0, 0x43);
- outb((CLOCK_TICK_RATE / (1000 / 50)) & 0xff, 0x42);
- outb((CLOCK_TICK_RATE / (1000 / 50)) >> 8, 0x42);
+ outb(latch & 0xff, 0x42);
+ outb(latch >> 8, 0x42);
tsc = t1 = t2 = get_cycles();
@@ -166,31 +212,154 @@ static unsigned long pit_calibrate_tsc(void)
/*
* Sanity checks:
*
- * If we were not able to read the PIT more than 5000
+ * If we were not able to read the PIT more than loopmin
* times, then we have been hit by a massive SMI
*
* If the maximum is 10 times larger than the minimum,
* then we got hit by an SMI as well.
*/
- if (pitcnt < 5000 || tscmax > 10 * tscmin)
+ if (pitcnt < loopmin || tscmax > 10 * tscmin)
return ULONG_MAX;
/* Calculate the PIT value */
delta = t2 - t1;
- do_div(delta, 50);
+ do_div(delta, ms);
return delta;
}
+/*
+ * This reads the current MSB of the PIT counter, and
+ * checks if we are running on sufficiently fast and
+ * non-virtualized hardware.
+ *
+ * Our expectations are:
+ *
+ * - the PIT is running at roughly 1.19MHz
+ *
+ * - each IO is going to take about 1us on real hardware,
+ * but we allow it to be much faster (by a factor of 10) or
+ * _slightly_ slower (ie we allow up to a 2us read+counter
+ * update - anything else implies a unacceptably slow CPU
+ * or PIT for the fast calibration to work.
+ *
+ * - with 256 PIT ticks to read the value, we have 214us to
+ * see the same MSB (and overhead like doing a single TSC
+ * read per MSB value etc).
+ *
+ * - We're doing 2 reads per loop (LSB, MSB), and we expect
+ * them each to take about a microsecond on real hardware.
+ * So we expect a count value of around 100. But we'll be
+ * generous, and accept anything over 50.
+ *
+ * - if the PIT is stuck, and we see *many* more reads, we
+ * return early (and the next caller of pit_expect_msb()
+ * then consider it a failure when they don't see the
+ * next expected value).
+ *
+ * These expectations mean that we know that we have seen the
+ * transition from one expected value to another with a fairly
+ * high accuracy, and we didn't miss any events. We can thus
+ * use the TSC value at the transitions to calculate a pretty
+ * good value for the TSC frequencty.
+ */
+static inline int pit_expect_msb(unsigned char val)
+{
+ int count = 0;
+
+ for (count = 0; count < 50000; count++) {
+ /* Ignore LSB */
+ inb(0x42);
+ if (inb(0x42) != val)
+ break;
+ }
+ return count > 50;
+}
+
+/*
+ * How many MSB values do we want to see? We aim for a
+ * 15ms calibration, which assuming a 2us counter read
+ * error should give us roughly 150 ppm precision for
+ * the calibration.
+ */
+#define QUICK_PIT_MS 15
+#define QUICK_PIT_ITERATIONS (QUICK_PIT_MS * PIT_TICK_RATE / 1000 / 256)
+
+static unsigned long quick_pit_calibrate(void)
+{
+ /* Set the Gate high, disable speaker */
+ outb((inb(0x61) & ~0x02) | 0x01, 0x61);
+
+ /*
+ * Counter 2, mode 0 (one-shot), binary count
+ *
+ * NOTE! Mode 2 decrements by two (and then the
+ * output is flipped each time, giving the same
+ * final output frequency as a decrement-by-one),
+ * so mode 0 is much better when looking at the
+ * individual counts.
+ */
+ outb(0xb0, 0x43);
+
+ /* Start at 0xffff */
+ outb(0xff, 0x42);
+ outb(0xff, 0x42);
+
+ if (pit_expect_msb(0xff)) {
+ int i;
+ u64 t1, t2, delta;
+ unsigned char expect = 0xfe;
+
+ t1 = get_cycles();
+ for (i = 0; i < QUICK_PIT_ITERATIONS; i++, expect--) {
+ if (!pit_expect_msb(expect))
+ goto failed;
+ }
+ t2 = get_cycles();
+
+ /*
+ * Make sure we can rely on the second TSC timestamp:
+ */
+ if (!pit_expect_msb(expect))
+ goto failed;
+
+ /*
+ * Ok, if we get here, then we've seen the
+ * MSB of the PIT decrement QUICK_PIT_ITERATIONS
+ * times, and each MSB had many hits, so we never
+ * had any sudden jumps.
+ *
+ * As a result, we can depend on there not being
+ * any odd delays anywhere, and the TSC reads are
+ * reliable.
+ *
+ * kHz = ticks / time-in-seconds / 1000;
+ * kHz = (t2 - t1) / (QPI * 256 / PIT_TICK_RATE) / 1000
+ * kHz = ((t2 - t1) * PIT_TICK_RATE) / (QPI * 256 * 1000)
+ */
+ delta = (t2 - t1)*PIT_TICK_RATE;
+ do_div(delta, QUICK_PIT_ITERATIONS*256*1000);
+ printk("Fast TSC calibration using PIT\n");
+ return delta;
+ }
+failed:
+ return 0;
+}
/**
* native_calibrate_tsc - calibrate the tsc on boot
*/
unsigned long native_calibrate_tsc(void)
{
- u64 tsc1, tsc2, delta, pm1, pm2, hpet1, hpet2;
+ u64 tsc1, tsc2, delta, ref1, ref2;
unsigned long tsc_pit_min = ULONG_MAX, tsc_ref_min = ULONG_MAX;
- unsigned long flags;
- int hpet = is_hpet_enabled(), i;
+ unsigned long flags, latch, ms, fast_calibrate;
+ int hpet = is_hpet_enabled(), i, loopmin;
+
+ local_irq_save(flags);
+ fast_calibrate = quick_pit_calibrate();
+ local_irq_restore(flags);
+ if (fast_calibrate)
+ return fast_calibrate;
/*
* Run 5 calibration loops to get the lowest frequency value
@@ -216,7 +385,13 @@ unsigned long native_calibrate_tsc(void)
* calibration delay loop as we have to wait for a certain
* amount of time anyway.
*/
- for (i = 0; i < 5; i++) {
+
+ /* Preset PIT loop values */
+ latch = CAL_LATCH;
+ ms = CAL_MS;
+ loopmin = CAL_PIT_LOOPS;
+
+ for (i = 0; i < 3; i++) {
unsigned long tsc_pit_khz;
/*
@@ -226,16 +401,16 @@ unsigned long native_calibrate_tsc(void)
* read the end value.
*/
local_irq_save(flags);
- tsc1 = tsc_read_refs(&pm1, hpet ? &hpet1 : NULL);
- tsc_pit_khz = pit_calibrate_tsc();
- tsc2 = tsc_read_refs(&pm2, hpet ? &hpet2 : NULL);
+ tsc1 = tsc_read_refs(&ref1, hpet);
+ tsc_pit_khz = pit_calibrate_tsc(latch, ms, loopmin);
+ tsc2 = tsc_read_refs(&ref2, hpet);
local_irq_restore(flags);
/* Pick the lowest PIT TSC calibration so far */
tsc_pit_min = min(tsc_pit_min, tsc_pit_khz);
/* hpet or pmtimer available ? */
- if (!hpet && !pm1 && !pm2)
+ if (!hpet && !ref1 && !ref2)
continue;
/* Check, whether the sampling was disturbed by an SMI */
@@ -243,23 +418,41 @@ unsigned long native_calibrate_tsc(void)
continue;
tsc2 = (tsc2 - tsc1) * 1000000LL;
+ if (hpet)
+ tsc2 = calc_hpet_ref(tsc2, ref1, ref2);
+ else
+ tsc2 = calc_pmtimer_ref(tsc2, ref1, ref2);
- if (hpet) {
- if (hpet2 < hpet1)
- hpet2 += 0x100000000ULL;
- hpet2 -= hpet1;
- tsc1 = ((u64)hpet2 * hpet_readl(HPET_PERIOD));
- do_div(tsc1, 1000000);
- } else {
- if (pm2 < pm1)
- pm2 += (u64)ACPI_PM_OVRRUN;
- pm2 -= pm1;
- tsc1 = pm2 * 1000000000LL;
- do_div(tsc1, PMTMR_TICKS_PER_SEC);
+ tsc_ref_min = min(tsc_ref_min, (unsigned long) tsc2);
+
+ /* Check the reference deviation */
+ delta = ((u64) tsc_pit_min) * 100;
+ do_div(delta, tsc_ref_min);
+
+ /*
+ * If both calibration results are inside a 10% window
+ * then we can be sure, that the calibration
+ * succeeded. We break out of the loop right away. We
+ * use the reference value, as it is more precise.
+ */
+ if (delta >= 90 && delta <= 110) {
+ printk(KERN_INFO
+ "TSC: PIT calibration matches %s. %d loops\n",
+ hpet ? "HPET" : "PMTIMER", i + 1);
+ return tsc_ref_min;
}
- do_div(tsc2, tsc1);
- tsc_ref_min = min(tsc_ref_min, (unsigned long) tsc2);
+ /*
+ * Check whether PIT failed more than once. This
+ * happens in virtualized environments. We need to
+ * give the virtual PC a slightly longer timeframe for
+ * the HPET/PMTIMER to make the result precise.
+ */
+ if (i == 1 && tsc_pit_min == ULONG_MAX) {
+ latch = CAL2_LATCH;
+ ms = CAL2_MS;
+ loopmin = CAL2_PIT_LOOPS;
+ }
}
/*
@@ -270,7 +463,7 @@ unsigned long native_calibrate_tsc(void)
printk(KERN_WARNING "TSC: Unable to calibrate against PIT\n");
/* We don't have an alternative source, disable TSC */
- if (!hpet && !pm1 && !pm2) {
+ if (!hpet && !ref1 && !ref2) {
printk("TSC: No reference (HPET/PMTIMER) available\n");
return 0;
}
@@ -278,7 +471,7 @@ unsigned long native_calibrate_tsc(void)
/* The alternative source failed as well, disable TSC */
if (tsc_ref_min == ULONG_MAX) {
printk(KERN_WARNING "TSC: HPET/PMTIMER calibration "
- "failed due to SMI disturbance.\n");
+ "failed.\n");
return 0;
}
@@ -290,44 +483,25 @@ unsigned long native_calibrate_tsc(void)
}
/* We don't have an alternative source, use the PIT calibration value */
- if (!hpet && !pm1 && !pm2) {
+ if (!hpet && !ref1 && !ref2) {
printk(KERN_INFO "TSC: Using PIT calibration value\n");
return tsc_pit_min;
}
/* The alternative source failed, use the PIT calibration value */
if (tsc_ref_min == ULONG_MAX) {
- printk(KERN_WARNING "TSC: HPET/PMTIMER calibration failed due "
- "to SMI disturbance. Using PIT calibration\n");
+ printk(KERN_WARNING "TSC: HPET/PMTIMER calibration failed. "
+ "Using PIT calibration\n");
return tsc_pit_min;
}
- /* Check the reference deviation */
- delta = ((u64) tsc_pit_min) * 100;
- do_div(delta, tsc_ref_min);
-
- /*
- * If both calibration results are inside a 5% window, the we
- * use the lower frequency of those as it is probably the
- * closest estimate.
- */
- if (delta >= 95 && delta <= 105) {
- printk(KERN_INFO "TSC: PIT calibration confirmed by %s.\n",
- hpet ? "HPET" : "PMTIMER");
- printk(KERN_INFO "TSC: using %s calibration value\n",
- tsc_pit_min <= tsc_ref_min ? "PIT" :
- hpet ? "HPET" : "PMTIMER");
- return tsc_pit_min <= tsc_ref_min ? tsc_pit_min : tsc_ref_min;
- }
-
- printk(KERN_WARNING "TSC: PIT calibration deviates from %s: %lu %lu.\n",
- hpet ? "HPET" : "PMTIMER", tsc_pit_min, tsc_ref_min);
-
/*
* The calibration values differ too much. In doubt, we use
* the PIT value as we know that there are PMTIMERs around
- * running at double speed.
+ * running at double speed. At least we let the user know:
*/
+ printk(KERN_WARNING "TSC: PIT calibration deviates from %s: %lu %lu.\n",
+ hpet ? "HPET" : "PMTIMER", tsc_pit_min, tsc_ref_min);
printk(KERN_INFO "TSC: Using PIT calibration value\n");
return tsc_pit_min;
}
@@ -585,7 +759,7 @@ __cpuinit int unsynchronized_tsc(void)
if (!cpu_has_tsc || tsc_unstable)
return 1;
-#ifdef CONFIG_SMP
+#ifdef CONFIG_X86_SMP
if (apic_is_clustered_box())
return 1;
#endif
@@ -639,10 +813,6 @@ void __init tsc_init(void)
cpu_khz = calibrate_cpu();
#endif
- lpj = ((u64)tsc_khz * 1000);
- do_div(lpj, HZ);
- lpj_fine = lpj;
-
printk("Detected %lu.%03lu MHz processor.\n",
(unsigned long)cpu_khz / 1000,
(unsigned long)cpu_khz % 1000);
@@ -662,6 +832,10 @@ void __init tsc_init(void)
/* now allow native_sched_clock() to use rdtsc */
tsc_disabled = 0;
+ lpj = ((u64)tsc_khz * 1000);
+ do_div(lpj, HZ);
+ lpj_fine = lpj;
+
use_tsc_delay();
/* Check and install the TSC clocksource */
dmi_check_system(bad_tsc_dmi_table);
generated by cgit v1.2.3-70-g09d2 (git 2.46.0) at 2025-11-04 05:16:06 +0000