aboutsummaryrefslogtreecommitdiff
path: root/arch/x86/kernel/tsc_64.c
blob: 01fc9f0c39e2031e403bbf2174eaeb18d24a483c (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/interrupt.h>
#include <linux/init.h>
#include <linux/clocksource.h>
#include <linux/time.h>
#include <linux/acpi.h>
#include <linux/cpufreq.h>
#include <linux/acpi_pmtmr.h>

#include <asm/hpet.h>
#include <asm/timex.h>
#include <asm/timer.h>
#include <asm/vgtod.h>

static int notsc __initdata = 0;

unsigned int cpu_khz;		/* TSC clocks / usec, not used here */
EXPORT_SYMBOL(cpu_khz);
unsigned int tsc_khz;
EXPORT_SYMBOL(tsc_khz);

/* Accelerators 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 precision, 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!"
 */
DEFINE_PER_CPU(unsigned long, cyc2ns);

static void set_cyc2ns_scale(unsigned long cpu_khz, int cpu)
{
	unsigned long flags, prev_scale, *scale;
	unsigned long long tsc_now, ns_now;

	local_irq_save(flags);
	sched_clock_idle_sleep_event();

	scale = &per_cpu(cyc2ns, cpu);

	rdtscll(tsc_now);
	ns_now = __cycles_2_ns(tsc_now);

	prev_scale = *scale;
	if (cpu_khz)
		*scale = (NSEC_PER_MSEC << CYC2NS_SCALE_FACTOR)/cpu_khz;

	sched_clock_idle_wakeup_event(0);
	local_irq_restore(flags);
}

unsigned long long native_sched_clock(void)
{
	unsigned long a = 0;

	/* Could do CPU core sync here. Opteron can execute rdtsc speculatively,
	 * which means it is not completely exact and may not be monotonous
	 * between CPUs. But the errors should be too small to matter for
	 * scheduling purposes.
	 */

	rdtscll(a);
	return cycles_2_ns(a);
}

/* We need to define a real function for sched_clock, to override the
   weak default version */
#ifdef CONFIG_PARAVIRT
unsigned long long sched_clock(void)
{
	return paravirt_sched_clock();
}
#else
unsigned long long
sched_clock(void) __attribute__((alias("native_sched_clock")));
#endif


static int tsc_unstable;

int check_tsc_unstable(void)
{
	return tsc_unstable;
}
EXPORT_SYMBOL_GPL(check_tsc_unstable);

#ifdef CONFIG_CPU_FREQ

/* Frequency scaling support. Adjust the TSC based timer when the cpu frequency
 * changes.
 *
 * RED-PEN: On SMP we assume all CPUs run with the same frequency.  It's
 * not that important because current Opteron setups do not support
 * scaling on SMP anyroads.
 *
 * Should fix up last_tsc too. Currently gettimeofday in the
 * first tick after the change will be slightly wrong.
 */

static unsigned int  ref_freq;
static unsigned long loops_per_jiffy_ref;
static unsigned long tsc_khz_ref;

static int time_cpufreq_notifier(struct notifier_block *nb, unsigned long val,
				 void *data)
{
	struct cpufreq_freqs *freq = data;
	unsigned long *lpj, dummy;

	if (cpu_has(&cpu_data(freq->cpu), X86_FEATURE_CONSTANT_TSC))
		return 0;

	lpj = &dummy;
	if (!(freq->flags & CPUFREQ_CONST_LOOPS))
#ifdef CONFIG_SMP
		lpj = &cpu_data(freq->cpu).loops_per_jiffy;
#else
		lpj = &boot_cpu_data.loops_per_jiffy;
#endif

	if (!ref_freq) {
		ref_freq = freq->old;
		loops_per_jiffy_ref = *lpj;
		tsc_khz_ref = tsc_khz;
	}
	if ((val == CPUFREQ_PRECHANGE  && freq->old < freq->new) ||
		(val == CPUFREQ_POSTCHANGE && freq->old > freq->new) ||
		(val == CPUFREQ_RESUMECHANGE)) {
		*lpj =
		cpufreq_scale(loops_per_jiffy_ref, ref_freq, freq->new);

		tsc_khz = cpufreq_scale(tsc_khz_ref, ref_freq, freq->new);
		if (!(freq->flags & CPUFREQ_CONST_LOOPS))
			mark_tsc_unstable("cpufreq changes");
	}

	preempt_disable();
	set_cyc2ns_scale(tsc_khz_ref, smp_processor_id());
	preempt_enable();

	return 0;
}

static struct notifier_block time_cpufreq_notifier_block = {
	.notifier_call  = time_cpufreq_notifier
};

static int __init cpufreq_tsc(void)
{
	cpufreq_register_notifier(&time_cpufreq_notifier_block,
				  CPUFREQ_TRANSITION_NOTIFIER);
	return 0;
}

core_initcall(cpufreq_tsc);

#endif

#define MAX_RETRIES	5
#define SMI_TRESHOLD	50000

/*
 * Read TSC and the reference counters. Take care of SMI disturbance
 */
static unsigned long __init tsc_read_refs(unsigned long *pm,
					  unsigned long *hpet)
{
	unsigned long t1, t2;
	int i;

	for (i = 0; i < MAX_RETRIES; i++) {
		t1 = get_cycles();
		if (hpet)
			*hpet = hpet_readl(HPET_COUNTER) & 0xFFFFFFFF;
		else
			*pm = acpi_pm_read_early();
		t2 = get_cycles();
		if ((t2 - t1) < SMI_TRESHOLD)
			return t2;
	}
	return ULONG_MAX;
}

/**
 * tsc_calibrate - calibrate the tsc on boot
 */
void __init tsc_calibrate(void)
{
	unsigned long flags, tsc1, tsc2, tr1, tr2, pm1, pm2, hpet1, hpet2;
	int hpet = is_hpet_enabled(), cpu;

	local_irq_save(flags);

	tsc1 = tsc_read_refs(&pm1, hpet ? &hpet1 : NULL);

	outb((inb(0x61) & ~0x02) | 0x01, 0x61);

	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();

	tsc2 = tsc_read_refs(&pm2, hpet ? &hpet2 : NULL);

	local_irq_restore(flags);

	/*
	 * Preset the result with the raw and inaccurate PIT
	 * calibration value
	 */
	tsc_khz = (tr2 - tr1) / 50;

	/* hpet or pmtimer available ? */
	if (!hpet && !pm1 && !pm2) {
		printk(KERN_INFO "TSC calibrated against PIT\n");
		return;
	}

	/* Check, whether the sampling was disturbed by an SMI */
	if (tsc1 == ULONG_MAX || tsc2 == ULONG_MAX) {
		printk(KERN_WARNING "TSC calibration disturbed by SMI, "
		       "using PIT calibration result\n");
		return;
	}

	tsc2 = (tsc2 - tsc1) * 1000000L;

	if (hpet) {
		printk(KERN_INFO "TSC calibrated against HPET\n");
		if (hpet2 < hpet1)
			hpet2 += 0x100000000;
		hpet2 -= hpet1;
		tsc1 = (hpet2 * hpet_readl(HPET_PERIOD)) / 1000000;
	} else {
		printk(KERN_INFO "TSC calibrated against PM_TIMER\n");
		if (pm2 < pm1)
			pm2 += ACPI_PM_OVRRUN;
		pm2 -= pm1;
		tsc1 = (pm2 * 1000000000) / PMTMR_TICKS_PER_SEC;
	}

	tsc_khz = tsc2 / tsc1;

	for_each_possible_cpu(cpu)
		set_cyc2ns_scale(tsc_khz, cpu);
}

/*
 * Make an educated guess if the TSC is trustworthy and synchronized
 * over all CPUs.
 */
__cpuinit int unsynchronized_tsc(void)
{
	if (tsc_unstable)
		return 1;

#ifdef CONFIG_SMP
	if (apic_is_clustered_box())
		return 1;
#endif

	if (boot_cpu_has(X86_FEATURE_CONSTANT_TSC))
		return 0;

	/* Assume multi socket systems are not synchronized */
	return num_present_cpus() > 1;
}

int __init notsc_setup(char *s)
{
	notsc = 1;
	return 1;
}

__setup("notsc", notsc_setup);

static struct clocksource clocksource_tsc;

/*
 * We compare the TSC to the cycle_last value in the clocksource
 * structure to avoid a nasty time-warp. This can be observed in a
 * very small window right after one CPU updated cycle_last under
 * xtime/vsyscall_gtod lock and the other CPU reads a TSC value which
 * is smaller than the cycle_last reference value due to a TSC which
 * is slighty behind. This delta is nowhere else observable, but in
 * that case it results in a forward time jump in the range of hours
 * due to the unsigned delta calculation of the time keeping core
 * code, which is necessary to support wrapping clocksources like pm
 * timer.
 */
static cycle_t read_tsc(void)
{
	cycle_t ret = (cycle_t)get_cycles();

	return ret >= clocksource_tsc.cycle_last ?
		ret : clocksource_tsc.cycle_last;
}

static cycle_t __vsyscall_fn vread_tsc(void)
{
	cycle_t ret = (cycle_t)vget_cycles();

	return ret >= __vsyscall_gtod_data.clock.cycle_last ?
		ret : __vsyscall_gtod_data.clock.cycle_last;
}

static struct clocksource clocksource_tsc = {
	.name			= "tsc",
	.rating			= 300,
	.read			= read_tsc,
	.mask			= CLOCKSOURCE_MASK(64),
	.shift			= 22,
	.flags			= CLOCK_SOURCE_IS_CONTINUOUS |
				  CLOCK_SOURCE_MUST_VERIFY,
	.vread			= vread_tsc,
};

void mark_tsc_unstable(char *reason)
{
	if (!tsc_unstable) {
		tsc_unstable = 1;
		printk("Marking TSC unstable due to %s\n", reason);
		/* Change only the rating, when not registered */
		if (clocksource_tsc.mult)
			clocksource_change_rating(&clocksource_tsc, 0);
		else
			clocksource_tsc.rating = 0;
	}
}
EXPORT_SYMBOL_GPL(mark_tsc_unstable);

void __init init_tsc_clocksource(void)
{
	if (!notsc) {
		clocksource_tsc.mult = clocksource_khz2mult(tsc_khz,
							clocksource_tsc.shift);
		if (check_tsc_unstable())
			clocksource_tsc.rating = 0;

		clocksource_register(&clocksource_tsc);
	}
}