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.c424
1 files changed, 369 insertions, 55 deletions
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 7603c055390..161bb850fc4 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -104,7 +104,7 @@ __setup("notsc", notsc_setup);
/*
* Read TSC and the reference counters. Take care of SMI disturbance
*/
-static u64 __init 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 __init 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;
@@ -122,80 +122,390 @@ static u64 __init tsc_read_refs(u64 *pm, u64 *hpet)
return ULLONG_MAX;
}
-/**
- * native_calibrate_tsc - calibrate the tsc on boot
+/*
+ * Calculate the TSC frequency from HPET reference
*/
-unsigned long native_calibrate_tsc(void)
+static unsigned long calc_hpet_ref(u64 deltatsc, u64 hpet1, u64 hpet2)
{
- unsigned long flags;
- u64 tsc1, tsc2, tr1, tr2, delta, pm1, pm2, hpet1, hpet2;
- int hpet = is_hpet_enabled();
- unsigned int tsc_khz_val = 0;
+ u64 tmp;
- local_irq_save(flags);
+ 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;
- tsc1 = tsc_read_refs(&pm1, hpet ? &hpet1 : NULL);
+ 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(u32 latch, unsigned long ms, int loopmin)
+{
+ u64 tsc, t1, t2, delta;
+ unsigned long tscmin, tscmax;
+ int pitcnt;
+ /* Set the Gate high, disable speaker */
outb((inb(0x61) & ~0x02) | 0x01, 0x61);
+ /*
+ * Setup CTC channel 2* for mode 0, (interrupt on terminal
+ * count mode), binary count. Set the latch register to 50ms
+ * (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);
- tr1 = get_cycles();
- while ((inb(0x61) & 0x20) == 0);
- tr2 = get_cycles();
+ outb(latch & 0xff, 0x42);
+ outb(latch >> 8, 0x42);
+
+ tsc = t1 = t2 = get_cycles();
+
+ pitcnt = 0;
+ tscmax = 0;
+ tscmin = ULONG_MAX;
+ while ((inb(0x61) & 0x20) == 0) {
+ t2 = get_cycles();
+ delta = t2 - tsc;
+ tsc = t2;
+ if ((unsigned long) delta < tscmin)
+ tscmin = (unsigned int) delta;
+ if ((unsigned long) delta > tscmax)
+ tscmax = (unsigned int) delta;
+ pitcnt++;
+ }
+
+ /*
+ * Sanity checks:
+ *
+ * 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 < loopmin || tscmax > 10 * tscmin)
+ return ULONG_MAX;
+
+ /* Calculate the PIT value */
+ delta = t2 - t1;
+ do_div(delta, ms);
+ return delta;
+}
- tsc2 = tsc_read_refs(&pm2, hpet ? &hpet2 : NULL);
+/*
+ * 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, ref1, ref2;
+ unsigned long tsc_pit_min = ULONG_MAX, tsc_ref_min = ULONG_MAX;
+ 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;
/*
- * Preset the result with the raw and inaccurate PIT
- * calibration value
+ * Run 5 calibration loops to get the lowest frequency value
+ * (the best estimate). We use two different calibration modes
+ * here:
+ *
+ * 1) PIT loop. We set the PIT Channel 2 to oneshot mode and
+ * load a timeout of 50ms. We read the time right after we
+ * started the timer and wait until the PIT count down reaches
+ * zero. In each wait loop iteration we read the TSC and check
+ * the delta to the previous read. We keep track of the min
+ * and max values of that delta. The delta is mostly defined
+ * by the IO time of the PIT access, so we can detect when a
+ * SMI/SMM disturbance happend between the two reads. If the
+ * maximum time is significantly larger than the minimum time,
+ * then we discard the result and have another try.
+ *
+ * 2) Reference counter. If available we use the HPET or the
+ * PMTIMER as a reference to check the sanity of that value.
+ * We use separate TSC readouts and check inside of the
+ * reference read for a SMI/SMM disturbance. We dicard
+ * disturbed values here as well. We do that around the PIT
+ * calibration delay loop as we have to wait for a certain
+ * amount of time anyway.
*/
- delta = (tr2 - tr1);
- do_div(delta, 50);
- tsc_khz_val = delta;
-
- /* hpet or pmtimer available ? */
- if (!hpet && !pm1 && !pm2) {
- printk(KERN_INFO "TSC calibrated against PIT\n");
- goto out;
+
+ /* 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;
+
+ /*
+ * Read the start value and the reference count of
+ * hpet/pmtimer when available. Then do the PIT
+ * calibration, which will take at least 50ms, and
+ * read the end value.
+ */
+ local_irq_save(flags);
+ 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 && !ref1 && !ref2)
+ continue;
+
+ /* Check, whether the sampling was disturbed by an SMI */
+ if (tsc1 == ULLONG_MAX || tsc2 == ULLONG_MAX)
+ continue;
+
+ tsc2 = (tsc2 - tsc1) * 1000000LL;
+ if (hpet)
+ tsc2 = calc_hpet_ref(tsc2, ref1, ref2);
+ else
+ tsc2 = calc_pmtimer_ref(tsc2, ref1, ref2);
+
+ 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;
+ }
+
+ /*
+ * 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;
+ }
}
- /* Check, whether the sampling was disturbed by an SMI */
- if (tsc1 == ULLONG_MAX || tsc2 == ULLONG_MAX) {
- printk(KERN_WARNING "TSC calibration disturbed by SMI, "
- "using PIT calibration result\n");
- goto out;
+ /*
+ * Now check the results.
+ */
+ if (tsc_pit_min == ULONG_MAX) {
+ /* PIT gave no useful value */
+ printk(KERN_WARNING "TSC: Unable to calibrate against PIT\n");
+
+ /* We don't have an alternative source, disable TSC */
+ if (!hpet && !ref1 && !ref2) {
+ printk("TSC: No reference (HPET/PMTIMER) available\n");
+ return 0;
+ }
+
+ /* The alternative source failed as well, disable TSC */
+ if (tsc_ref_min == ULONG_MAX) {
+ printk(KERN_WARNING "TSC: HPET/PMTIMER calibration "
+ "failed.\n");
+ return 0;
+ }
+
+ /* Use the alternative source */
+ printk(KERN_INFO "TSC: using %s reference calibration\n",
+ hpet ? "HPET" : "PMTIMER");
+
+ return tsc_ref_min;
}
- tsc2 = (tsc2 - tsc1) * 1000000LL;
-
- if (hpet) {
- printk(KERN_INFO "TSC calibrated against HPET\n");
- if (hpet2 < hpet1)
- hpet2 += 0x100000000ULL;
- hpet2 -= hpet1;
- tsc1 = ((u64)hpet2 * hpet_readl(HPET_PERIOD));
- do_div(tsc1, 1000000);
- } else {
- printk(KERN_INFO "TSC calibrated against PM_TIMER\n");
- if (pm2 < pm1)
- pm2 += (u64)ACPI_PM_OVRRUN;
- pm2 -= pm1;
- tsc1 = pm2 * 1000000000LL;
- do_div(tsc1, PMTMR_TICKS_PER_SEC);
+ /* We don't have an alternative source, use the PIT calibration value */
+ if (!hpet && !ref1 && !ref2) {
+ printk(KERN_INFO "TSC: Using PIT calibration value\n");
+ return tsc_pit_min;
}
- do_div(tsc2, tsc1);
- tsc_khz_val = tsc2;
+ /* The alternative source failed, use the PIT calibration value */
+ if (tsc_ref_min == ULONG_MAX) {
+ printk(KERN_WARNING "TSC: HPET/PMTIMER calibration failed. "
+ "Using PIT calibration\n");
+ return tsc_pit_min;
+ }
-out:
- return tsc_khz_val;
+ /*
+ * 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. 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;
}
-
#ifdef CONFIG_X86_32
/* Only called from the Powernow K7 cpu freq driver */
int recalibrate_cpu_khz(void)
@@ -314,7 +624,7 @@ static int time_cpufreq_notifier(struct notifier_block *nb, unsigned long val,
mark_tsc_unstable("cpufreq changes");
}
- set_cyc2ns_scale(tsc_khz_ref, freq->cpu);
+ set_cyc2ns_scale(tsc_khz, freq->cpu);
return 0;
}
@@ -325,6 +635,10 @@ static struct notifier_block time_cpufreq_notifier_block = {
static int __init cpufreq_tsc(void)
{
+ if (!cpu_has_tsc)
+ return 0;
+ if (boot_cpu_has(X86_FEATURE_CONSTANT_TSC))
+ return 0;
cpufreq_register_notifier(&time_cpufreq_notifier_block,
CPUFREQ_TRANSITION_NOTIFIER);
return 0;
generated by cgit v1.2.3 (git 2.25.1) at 2024-11-01 00:25:54 +0000