xref: /freebsd/sys/x86/x86/tsc.c (revision b2c63698)

/*-
 * Copyright (c) 1998-2003 Poul-Henning Kamp
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");

#include "opt_compat.h"
#include "opt_clock.h"

#include <sys/param.h>
#include <sys/bus.h>
#include <sys/cpu.h>
#include <sys/limits.h>
#include <sys/malloc.h>
#include <sys/systm.h>
#include <sys/sysctl.h>
#include <sys/time.h>
#include <sys/timetc.h>
#include <sys/kernel.h>
#include <sys/power.h>
#include <sys/smp.h>
#include <sys/vdso.h>
#include <machine/clock.h>
#include <machine/cputypes.h>
#include <machine/md_var.h>
#include <machine/specialreg.h>

#include "cpufreq_if.h"

uint64_t	tsc_freq;
int		tsc_is_invariant;
int		tsc_perf_stat;

static eventhandler_tag tsc_levels_tag, tsc_pre_tag, tsc_post_tag;

SYSCTL_INT(_kern_timecounter, OID_AUTO, invariant_tsc, CTLFLAG_RDTUN,
    &tsc_is_invariant, 0, "Indicates whether the TSC is P-state invariant");
TUNABLE_INT("kern.timecounter.invariant_tsc", &tsc_is_invariant);

#ifdef SMP
int	smp_tsc;
SYSCTL_INT(_kern_timecounter, OID_AUTO, smp_tsc, CTLFLAG_RDTUN, &smp_tsc, 0,
    "Indicates whether the TSC is safe to use in SMP mode");
TUNABLE_INT("kern.timecounter.smp_tsc", &smp_tsc);

int	smp_tsc_adjust = 0;
SYSCTL_INT(_kern_timecounter, OID_AUTO, smp_tsc_adjust, CTLFLAG_RDTUN,
    &smp_tsc_adjust, 0, "Try to adjust TSC on APs to match BSP");
TUNABLE_INT("kern.timecounter.smp_tsc_adjust", &smp_tsc_adjust);
#endif

static int	tsc_shift = 1;
SYSCTL_INT(_kern_timecounter, OID_AUTO, tsc_shift, CTLFLAG_RDTUN,
    &tsc_shift, 0, "Shift to pre-apply for the maximum TSC frequency");
TUNABLE_INT("kern.timecounter.tsc_shift", &tsc_shift);

static int	tsc_disabled;
SYSCTL_INT(_machdep, OID_AUTO, disable_tsc, CTLFLAG_RDTUN, &tsc_disabled, 0,
    "Disable x86 Time Stamp Counter");
TUNABLE_INT("machdep.disable_tsc", &tsc_disabled);

static int	tsc_skip_calibration;
SYSCTL_INT(_machdep, OID_AUTO, disable_tsc_calibration, CTLFLAG_RDTUN,
    &tsc_skip_calibration, 0, "Disable TSC frequency calibration");
TUNABLE_INT("machdep.disable_tsc_calibration", &tsc_skip_calibration);

static void tsc_freq_changed(void *arg, const struct cf_level *level,
    int status);
static void tsc_freq_changing(void *arg, const struct cf_level *level,
    int *status);
static unsigned tsc_get_timecount(struct timecounter *tc);
static inline unsigned tsc_get_timecount_low(struct timecounter *tc);
static unsigned tsc_get_timecount_lfence(struct timecounter *tc);
static unsigned tsc_get_timecount_low_lfence(struct timecounter *tc);
static unsigned tsc_get_timecount_mfence(struct timecounter *tc);
static unsigned tsc_get_timecount_low_mfence(struct timecounter *tc);
static void tsc_levels_changed(void *arg, int unit);

static struct timecounter tsc_timecounter = {
	tsc_get_timecount,	/* get_timecount */
	0,			/* no poll_pps */
	~0u,			/* counter_mask */
	0,			/* frequency */
	"TSC",			/* name */
	800,			/* quality (adjusted in code) */
};

#define	VMW_HVMAGIC		0x564d5868
#define	VMW_HVPORT		0x5658
#define	VMW_HVCMD_GETVERSION	10
#define	VMW_HVCMD_GETHZ		45

static __inline void
vmware_hvcall(u_int cmd, u_int *p)
{

	__asm __volatile("inl %w3, %0"
	: "=a" (p[0]), "=b" (p[1]), "=c" (p[2]), "=d" (p[3])
	: "0" (VMW_HVMAGIC), "1" (UINT_MAX), "2" (cmd), "3" (VMW_HVPORT)
	: "memory");
}

static int
tsc_freq_vmware(void)
{
	char hv_sig[13];
	u_int regs[4];
	char *p;
	u_int hv_high;
	int i;

	/*
	 * [RFC] CPUID usage for interaction between Hypervisors and Linux.
	 * http://lkml.org/lkml/2008/10/1/246
	 *
	 * KB1009458: Mechanisms to determine if software is running in
	 * a VMware virtual machine
	 * http://kb.vmware.com/kb/1009458
	 */
	hv_high = 0;
	if ((cpu_feature2 & CPUID2_HV) != 0) {
		do_cpuid(0x40000000, regs);
		hv_high = regs[0];
		for (i = 1, p = hv_sig; i < 4; i++, p += sizeof(regs) / 4)
			memcpy(p, &regs[i], sizeof(regs[i]));
		*p = '\0';
		if (bootverbose) {
			/*
			 * HV vendor	ID string
			 * ------------+--------------
			 * KVM		"KVMKVMKVM"
			 * Microsoft	"Microsoft Hv"
			 * VMware	"VMwareVMware"
			 * Xen		"XenVMMXenVMM"
			 */
			printf("Hypervisor: Origin = \"%s\"\n", hv_sig);
		}
		if (strncmp(hv_sig, "VMwareVMware", 12) != 0)
			return (0);
	} else {
		p = getenv("smbios.system.serial");
		if (p == NULL)
			return (0);
		if (strncmp(p, "VMware-", 7) != 0 &&
		    strncmp(p, "VMW", 3) != 0) {
			freeenv(p);
			return (0);
		}
		freeenv(p);
		vmware_hvcall(VMW_HVCMD_GETVERSION, regs);
		if (regs[1] != VMW_HVMAGIC)
			return (0);
	}
	if (hv_high >= 0x40000010) {
		do_cpuid(0x40000010, regs);
		tsc_freq = regs[0] * 1000;
	} else {
		vmware_hvcall(VMW_HVCMD_GETHZ, regs);
		if (regs[1] != UINT_MAX)
			tsc_freq = regs[0] | ((uint64_t)regs[1] << 32);
	}
	tsc_is_invariant = 1;
	return (1);
}

static void
tsc_freq_intel(void)
{
	char brand[48];
	u_int regs[4];
	uint64_t freq;
	char *p;
	u_int i;

	/*
	 * Intel Processor Identification and the CPUID Instruction
	 * Application Note 485.
	 * http://www.intel.com/assets/pdf/appnote/241618.pdf
	 */
	if (cpu_exthigh >= 0x80000004) {
		p = brand;
		for (i = 0x80000002; i < 0x80000005; i++) {
			do_cpuid(i, regs);
			memcpy(p, regs, sizeof(regs));
			p += sizeof(regs);
		}
		p = NULL;
		for (i = 0; i < sizeof(brand) - 1; i++)
			if (brand[i] == 'H' && brand[i + 1] == 'z')
				p = brand + i;
		if (p != NULL) {
			p -= 5;
			switch (p[4]) {
			case 'M':
				i = 1;
				break;
			case 'G':
				i = 1000;
				break;
			case 'T':
				i = 1000000;
				break;
			default:
				return;
			}
#define	C2D(c)	((c) - '0')
			if (p[1] == '.') {
				freq = C2D(p[0]) * 1000;
				freq += C2D(p[2]) * 100;
				freq += C2D(p[3]) * 10;
				freq *= i * 1000;
			} else {
				freq = C2D(p[0]) * 1000;
				freq += C2D(p[1]) * 100;
				freq += C2D(p[2]) * 10;
				freq += C2D(p[3]);
				freq *= i * 1000000;
			}
#undef C2D
			tsc_freq = freq;
		}
	}
}

static void
probe_tsc_freq(void)
{
	u_int regs[4];
	uint64_t tsc1, tsc2;

	if (cpu_high >= 6) {
		do_cpuid(6, regs);
		if ((regs[2] & CPUID_PERF_STAT) != 0) {
			/*
			 * XXX Some emulators expose host CPUID without actual
			 * support for these MSRs.  We must test whether they
			 * really work.
			 */
			wrmsr(MSR_MPERF, 0);
			wrmsr(MSR_APERF, 0);
			DELAY(10);
			if (rdmsr(MSR_MPERF) > 0 && rdmsr(MSR_APERF) > 0)
				tsc_perf_stat = 1;
		}
	}

	if (tsc_freq_vmware())
		return;

	switch (cpu_vendor_id) {
	case CPU_VENDOR_AMD:
		if ((amd_pminfo & AMDPM_TSC_INVARIANT) != 0 ||
		    (vm_guest == VM_GUEST_NO &&
		    CPUID_TO_FAMILY(cpu_id) >= 0x10))
			tsc_is_invariant = 1;
		if (cpu_feature & CPUID_SSE2) {
			tsc_timecounter.tc_get_timecount =
			    tsc_get_timecount_mfence;
		}
		break;
	case CPU_VENDOR_INTEL:
		if ((amd_pminfo & AMDPM_TSC_INVARIANT) != 0 ||
		    (vm_guest == VM_GUEST_NO &&
		    ((CPUID_TO_FAMILY(cpu_id) == 0x6 &&
		    CPUID_TO_MODEL(cpu_id) >= 0xe) ||
		    (CPUID_TO_FAMILY(cpu_id) == 0xf &&
		    CPUID_TO_MODEL(cpu_id) >= 0x3))))
			tsc_is_invariant = 1;
		if (cpu_feature & CPUID_SSE2) {
			tsc_timecounter.tc_get_timecount =
			    tsc_get_timecount_lfence;
		}
		break;
	case CPU_VENDOR_CENTAUR:
		if (vm_guest == VM_GUEST_NO &&
		    CPUID_TO_FAMILY(cpu_id) == 0x6 &&
		    CPUID_TO_MODEL(cpu_id) >= 0xf &&
		    (rdmsr(0x1203) & 0x100000000ULL) == 0)
			tsc_is_invariant = 1;
		if (cpu_feature & CPUID_SSE2) {
			tsc_timecounter.tc_get_timecount =
			    tsc_get_timecount_lfence;
		}
		break;
	}

	if (tsc_skip_calibration) {
		if (cpu_vendor_id == CPU_VENDOR_INTEL)
			tsc_freq_intel();
		return;
	}

	if (bootverbose)
	        printf("Calibrating TSC clock ... ");
	tsc1 = rdtsc();
	DELAY(1000000);
	tsc2 = rdtsc();
	tsc_freq = tsc2 - tsc1;
	if (bootverbose)
		printf("TSC clock: %ju Hz\n", (intmax_t)tsc_freq);
}

void
init_TSC(void)
{

	if ((cpu_feature & CPUID_TSC) == 0 || tsc_disabled)
		return;

	probe_tsc_freq();

	/*
	 * Inform CPU accounting about our boot-time clock rate.  This will
	 * be updated if someone loads a cpufreq driver after boot that
	 * discovers a new max frequency.
	 */
	if (tsc_freq != 0)
		set_cputicker(rdtsc, tsc_freq, !tsc_is_invariant);

	if (tsc_is_invariant)
		return;

	/* Register to find out about changes in CPU frequency. */
	tsc_pre_tag = EVENTHANDLER_REGISTER(cpufreq_pre_change,
	    tsc_freq_changing, NULL, EVENTHANDLER_PRI_FIRST);
	tsc_post_tag = EVENTHANDLER_REGISTER(cpufreq_post_change,
	    tsc_freq_changed, NULL, EVENTHANDLER_PRI_FIRST);
	tsc_levels_tag = EVENTHANDLER_REGISTER(cpufreq_levels_changed,
	    tsc_levels_changed, NULL, EVENTHANDLER_PRI_ANY);
}

#ifdef SMP

/*
 * RDTSC is not a serializing instruction, and does not drain
 * instruction stream, so we need to drain the stream before executing
 * it.  It could be fixed by use of RDTSCP, except the instruction is
 * not available everywhere.
 *
 * Use CPUID for draining in the boot-time SMP constistency test.  The
 * timecounters use MFENCE for AMD CPUs, and LFENCE for others (Intel
 * and VIA) when SSE2 is present, and nothing on older machines which
 * also do not issue RDTSC prematurely.  There, testing for SSE2 and
 * vendor is too cumbersome, and we learn about TSC presence from CPUID.
 *
 * Do not use do_cpuid(), since we do not need CPUID results, which
 * have to be written into memory with do_cpuid().
 */
#define	TSC_READ(x)							\
static void								\
tsc_read_##x(void *arg)							\
{									\
	uint64_t *tsc = arg;						\
	u_int cpu = PCPU_GET(cpuid);					\
									\
	__asm __volatile("cpuid" : : : "eax", "ebx", "ecx", "edx");	\
	tsc[cpu * 3 + x] = rdtsc();					\
}
TSC_READ(0)
TSC_READ(1)
TSC_READ(2)
#undef TSC_READ

#define	N	1000

static void
comp_smp_tsc(void *arg)
{
	uint64_t *tsc;
	int64_t d1, d2;
	u_int cpu = PCPU_GET(cpuid);
	u_int i, j, size;

	size = (mp_maxid + 1) * 3;
	for (i = 0, tsc = arg; i < N; i++, tsc += size)
		CPU_FOREACH(j) {
			if (j == cpu)
				continue;
			d1 = tsc[cpu * 3 + 1] - tsc[j * 3];
			d2 = tsc[cpu * 3 + 2] - tsc[j * 3 + 1];
			if (d1 <= 0 || d2 <= 0) {
				smp_tsc = 0;
				return;
			}
		}
}

static void
adj_smp_tsc(void *arg)
{
	uint64_t *tsc;
	int64_t d, min, max;
	u_int cpu = PCPU_GET(cpuid);
	u_int first, i, size;

	first = CPU_FIRST();
	if (cpu == first)
		return;
	min = INT64_MIN;
	max = INT64_MAX;
	size = (mp_maxid + 1) * 3;
	for (i = 0, tsc = arg; i < N; i++, tsc += size) {
		d = tsc[first * 3] - tsc[cpu * 3 + 1];
		if (d > min)
			min = d;
		d = tsc[first * 3 + 1] - tsc[cpu * 3 + 2];
		if (d > min)
			min = d;
		d = tsc[first * 3 + 1] - tsc[cpu * 3];
		if (d < max)
			max = d;
		d = tsc[first * 3 + 2] - tsc[cpu * 3 + 1];
		if (d < max)
			max = d;
	}
	if (min > max)
		return;
	d = min / 2 + max / 2;
	__asm __volatile (
		"movl $0x10, %%ecx\n\t"
		"rdmsr\n\t"
		"addl %%edi, %%eax\n\t"
		"adcl %%esi, %%edx\n\t"
		"wrmsr\n"
		: /* No output */
		: "D" ((uint32_t)d), "S" ((uint32_t)(d >> 32))
		: "ax", "cx", "dx", "cc"
	);
}

static int
test_tsc(void)
{
	uint64_t *data, *tsc;
	u_int i, size, adj;

	if ((!smp_tsc && !tsc_is_invariant) || vm_guest)
		return (-100);
	size = (mp_maxid + 1) * 3;
	data = malloc(sizeof(*data) * size * N, M_TEMP, M_WAITOK);
	adj = 0;
retry:
	for (i = 0, tsc = data; i < N; i++, tsc += size)
		smp_rendezvous(tsc_read_0, tsc_read_1, tsc_read_2, tsc);
	smp_tsc = 1;	/* XXX */
	smp_rendezvous(smp_no_rendevous_barrier, comp_smp_tsc,
	    smp_no_rendevous_barrier, data);
	if (!smp_tsc && adj < smp_tsc_adjust) {
		adj++;
		smp_rendezvous(smp_no_rendevous_barrier, adj_smp_tsc,
		    smp_no_rendevous_barrier, data);
		goto retry;
	}
	free(data, M_TEMP);
	if (bootverbose)
		printf("SMP: %sed TSC synchronization test%s\n",
		    smp_tsc ? "pass" : "fail",
		    adj > 0 ? " after adjustment" : "");
	if (smp_tsc && tsc_is_invariant) {
		switch (cpu_vendor_id) {
		case CPU_VENDOR_AMD:
			/*
			 * Starting with Family 15h processors, TSC clock
			 * source is in the north bridge.  Check whether
			 * we have a single-socket/multi-core platform.
			 * XXX Need more work for complex cases.
			 */
			if (CPUID_TO_FAMILY(cpu_id) < 0x15 ||
			    (amd_feature2 & AMDID2_CMP) == 0 ||
			    smp_cpus > (cpu_procinfo2 & AMDID_CMP_CORES) + 1)
				break;
			return (1000);
		case CPU_VENDOR_INTEL:
			/*
			 * XXX Assume Intel platforms have synchronized TSCs.
			 */
			return (1000);
		}
		return (800);
	}
	return (-100);
}

#undef N

#else

/*
 * The function is not called, it is provided to avoid linking failure
 * on uniprocessor kernel.
 */
static int
test_tsc(void)
{

	return (0);
}

#endif /* SMP */

static void
init_TSC_tc(void)
{
	uint64_t max_freq;
	int shift;

	if ((cpu_feature & CPUID_TSC) == 0 || tsc_disabled)
		return;

	/*
	 * Limit timecounter frequency to fit in an int and prevent it from
	 * overflowing too fast.
	 */
	max_freq = UINT_MAX;

	/*
	 * We can not use the TSC if we support APM.  Precise timekeeping
	 * on an APM'ed machine is at best a fools pursuit, since
	 * any and all of the time spent in various SMM code can't
	 * be reliably accounted for.  Reading the RTC is your only
	 * source of reliable time info.  The i8254 loses too, of course,
	 * but we need to have some kind of time...
	 * We don't know at this point whether APM is going to be used
	 * or not, nor when it might be activated.  Play it safe.
	 */
	if (power_pm_get_type() == POWER_PM_TYPE_APM) {
		tsc_timecounter.tc_quality = -1000;
		if (bootverbose)
			printf("TSC timecounter disabled: APM enabled.\n");
		goto init;
	}

	/*
	 * We cannot use the TSC if it stops incrementing in deep sleep.
	 * Currently only Intel CPUs are known for this problem unless
	 * the invariant TSC bit is set.
	 */
	if (cpu_can_deep_sleep && cpu_vendor_id == CPU_VENDOR_INTEL &&
	    (amd_pminfo & AMDPM_TSC_INVARIANT) == 0) {
		tsc_timecounter.tc_quality = -1000;
		tsc_timecounter.tc_flags |= TC_FLAGS_C3STOP;
		if (bootverbose)
			printf("TSC timecounter disabled: C3 enabled.\n");
		goto init;
	}

	/*
	 * We can not use the TSC in SMP mode unless the TSCs on all CPUs
	 * are synchronized.  If the user is sure that the system has
	 * synchronized TSCs, set kern.timecounter.smp_tsc tunable to a
	 * non-zero value.  The TSC seems unreliable in virtualized SMP
	 * environments, so it is set to a negative quality in those cases.
	 */
	if (mp_ncpus > 1)
		tsc_timecounter.tc_quality = test_tsc();
	else if (tsc_is_invariant)
		tsc_timecounter.tc_quality = 1000;
	max_freq >>= tsc_shift;

init:
	for (shift = 0; shift <= 31 && (tsc_freq >> shift) > max_freq; shift++)
		;
	if ((cpu_feature & CPUID_SSE2) != 0 && mp_ncpus > 1) {
		if (cpu_vendor_id == CPU_VENDOR_AMD) {
			tsc_timecounter.tc_get_timecount = shift > 0 ?
			    tsc_get_timecount_low_mfence :
			    tsc_get_timecount_mfence;
		} else {
			tsc_timecounter.tc_get_timecount = shift > 0 ?
			    tsc_get_timecount_low_lfence :
			    tsc_get_timecount_lfence;
		}
	} else {
		tsc_timecounter.tc_get_timecount = shift > 0 ?
		    tsc_get_timecount_low : tsc_get_timecount;
	}
	if (shift > 0) {
		tsc_timecounter.tc_name = "TSC-low";
		if (bootverbose)
			printf("TSC timecounter discards lower %d bit(s)\n",
			    shift);
	}
	if (tsc_freq != 0) {
		tsc_timecounter.tc_frequency = tsc_freq >> shift;
		tsc_timecounter.tc_priv = (void *)(intptr_t)shift;
		tc_init(&tsc_timecounter);
	}
}
SYSINIT(tsc_tc, SI_SUB_SMP, SI_ORDER_ANY, init_TSC_tc, NULL);

/*
 * When cpufreq levels change, find out about the (new) max frequency.  We
 * use this to update CPU accounting in case it got a lower estimate at boot.
 */
static void
tsc_levels_changed(void *arg, int unit)
{
	device_t cf_dev;
	struct cf_level *levels;
	int count, error;
	uint64_t max_freq;

	/* Only use values from the first CPU, assuming all are equal. */
	if (unit != 0)
		return;

	/* Find the appropriate cpufreq device instance. */
	cf_dev = devclass_get_device(devclass_find("cpufreq"), unit);
	if (cf_dev == NULL) {
		printf("tsc_levels_changed() called but no cpufreq device?\n");
		return;
	}

	/* Get settings from the device and find the max frequency. */
	count = 64;
	levels = malloc(count * sizeof(*levels), M_TEMP, M_NOWAIT);
	if (levels == NULL)
		return;
	error = CPUFREQ_LEVELS(cf_dev, levels, &count);
	if (error == 0 && count != 0) {
		max_freq = (uint64_t)levels[0].total_set.freq * 1000000;
		set_cputicker(rdtsc, max_freq, 1);
	} else
		printf("tsc_levels_changed: no max freq found\n");
	free(levels, M_TEMP);
}

/*
 * If the TSC timecounter is in use, veto the pending change.  It may be
 * possible in the future to handle a dynamically-changing timecounter rate.
 */
static void
tsc_freq_changing(void *arg, const struct cf_level *level, int *status)
{

	if (*status != 0 || timecounter != &tsc_timecounter)
		return;

	printf("timecounter TSC must not be in use when "
	    "changing frequencies; change denied\n");
	*status = EBUSY;
}

/* Update TSC freq with the value indicated by the caller. */
static void
tsc_freq_changed(void *arg, const struct cf_level *level, int status)
{
	uint64_t freq;

	/* If there was an error during the transition, don't do anything. */
	if (tsc_disabled || status != 0)
		return;

	/* Total setting for this level gives the new frequency in MHz. */
	freq = (uint64_t)level->total_set.freq * 1000000;
	atomic_store_rel_64(&tsc_freq, freq);
	tsc_timecounter.tc_frequency =
	    freq >> (int)(intptr_t)tsc_timecounter.tc_priv;
}

static int
sysctl_machdep_tsc_freq(SYSCTL_HANDLER_ARGS)
{
	int error;
	uint64_t freq;

	freq = atomic_load_acq_64(&tsc_freq);
	if (freq == 0)
		return (EOPNOTSUPP);
	error = sysctl_handle_64(oidp, &freq, 0, req);
	if (error == 0 && req->newptr != NULL) {
		atomic_store_rel_64(&tsc_freq, freq);
		atomic_store_rel_64(&tsc_timecounter.tc_frequency,
		    freq >> (int)(intptr_t)tsc_timecounter.tc_priv);
	}
	return (error);
}

SYSCTL_PROC(_machdep, OID_AUTO, tsc_freq, CTLTYPE_U64 | CTLFLAG_RW,
    0, 0, sysctl_machdep_tsc_freq, "QU", "Time Stamp Counter frequency");

static u_int
tsc_get_timecount(struct timecounter *tc __unused)
{

	return (rdtsc32());
}

static inline u_int
tsc_get_timecount_low(struct timecounter *tc)
{
	uint32_t rv;

	__asm __volatile("rdtsc; shrd %%cl, %%edx, %0"
	    : "=a" (rv) : "c" ((int)(intptr_t)tc->tc_priv) : "edx");
	return (rv);
}

static u_int
tsc_get_timecount_lfence(struct timecounter *tc __unused)
{

	lfence();
	return (rdtsc32());
}

static u_int
tsc_get_timecount_low_lfence(struct timecounter *tc)
{

	lfence();
	return (tsc_get_timecount_low(tc));
}

static u_int
tsc_get_timecount_mfence(struct timecounter *tc __unused)
{

	mfence();
	return (rdtsc32());
}

static u_int
tsc_get_timecount_low_mfence(struct timecounter *tc)
{

	mfence();
	return (tsc_get_timecount_low(tc));
}

uint32_t
cpu_fill_vdso_timehands(struct vdso_timehands *vdso_th)
{

	vdso_th->th_x86_shift = (int)(intptr_t)timecounter->tc_priv;
	bzero(vdso_th->th_res, sizeof(vdso_th->th_res));
	return (timecounter == &tsc_timecounter);
}

#ifdef COMPAT_FREEBSD32
uint32_t
cpu_fill_vdso_timehands32(struct vdso_timehands32 *vdso_th32)
{

	vdso_th32->th_x86_shift = (int)(intptr_t)timecounter->tc_priv;
	bzero(vdso_th32->th_res, sizeof(vdso_th32->th_res));
	return (timecounter == &tsc_timecounter);
}
#endif