[net-next-2.6.git] / arch / x86 / kernel / pvclock.c

/*  paravirtual clock -- common code used by kvm/xen

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
*/

#include <linux/kernel.h>
#include <linux/percpu.h>
#include <asm/pvclock.h>

/*
 * These are perodically updated
 *    xen: magic shared_info page
 *    kvm: gpa registered via msr
 * and then copied here.
 */
struct pvclock_shadow_time {
	u64 tsc_timestamp;     /* TSC at last update of time vals.  */
	u64 system_timestamp;  /* Time, in nanosecs, since boot.    */
	u32 tsc_to_nsec_mul;
	int tsc_shift;
	u32 version;
	u8  flags;
};

static u8 valid_flags __read_mostly = 0;

void pvclock_set_flags(u8 flags)
{
	valid_flags = flags;
}

static u64 pvclock_get_nsec_offset(struct pvclock_shadow_time *shadow)
{
	u64 delta = native_read_tsc() - shadow->tsc_timestamp;
	return pvclock_scale_delta(delta, shadow->tsc_to_nsec_mul,
				   shadow->tsc_shift);
}

/*
 * Reads a consistent set of time-base values from hypervisor,
 * into a shadow data area.
 */
static unsigned pvclock_get_time_values(struct pvclock_shadow_time *dst,
					struct pvclock_vcpu_time_info *src)
{
	do {
		dst->version = src->version;
		rmb();		/* fetch version before data */
		dst->tsc_timestamp     = src->tsc_timestamp;
		dst->system_timestamp  = src->system_time;
		dst->tsc_to_nsec_mul   = src->tsc_to_system_mul;
		dst->tsc_shift         = src->tsc_shift;
		dst->flags             = src->flags;
		rmb();		/* test version after fetching data */
	} while ((src->version & 1) || (dst->version != src->version));

	return dst->version;
}

unsigned long pvclock_tsc_khz(struct pvclock_vcpu_time_info *src)
{
	u64 pv_tsc_khz = 1000000ULL << 32;

	do_div(pv_tsc_khz, src->tsc_to_system_mul);
	if (src->tsc_shift < 0)
		pv_tsc_khz <<= -src->tsc_shift;
	else
		pv_tsc_khz >>= src->tsc_shift;
	return pv_tsc_khz;
}

static atomic64_t last_value = ATOMIC64_INIT(0);

cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src)
{
	struct pvclock_shadow_time shadow;
	unsigned version;
	cycle_t ret, offset;
	u64 last;

	do {
		version = pvclock_get_time_values(&shadow, src);
		barrier();
		offset = pvclock_get_nsec_offset(&shadow);
		ret = shadow.system_timestamp + offset;
		barrier();
	} while (version != src->version);

	if ((valid_flags & PVCLOCK_TSC_STABLE_BIT) &&
		(shadow.flags & PVCLOCK_TSC_STABLE_BIT))
		return ret;

	/*
	 * Assumption here is that last_value, a global accumulator, always goes
	 * forward. If we are less than that, we should not be much smaller.
	 * We assume there is an error marging we're inside, and then the correction
	 * does not sacrifice accuracy.
	 *
	 * For reads: global may have changed between test and return,
	 * but this means someone else updated poked the clock at a later time.
	 * We just need to make sure we are not seeing a backwards event.
	 *
	 * For updates: last_value = ret is not enough, since two vcpus could be
	 * updating at the same time, and one of them could be slightly behind,
	 * making the assumption that last_value always go forward fail to hold.
	 */
	last = atomic64_read(&last_value);
	do {
		if (ret < last)
			return last;
		last = atomic64_cmpxchg(&last_value, last, ret);
	} while (unlikely(last != ret));

	return ret;
}

void pvclock_read_wallclock(struct pvclock_wall_clock *wall_clock,
			    struct pvclock_vcpu_time_info *vcpu_time,
			    struct timespec *ts)
{
	u32 version;
	u64 delta;
	struct timespec now;

	/* get wallclock at system boot */
	do {
		version = wall_clock->version;
		rmb();		/* fetch version before time */
		now.tv_sec  = wall_clock->sec;
		now.tv_nsec = wall_clock->nsec;
		rmb();		/* fetch time before checking version */
	} while ((wall_clock->version & 1) || (version != wall_clock->version));

	delta = pvclock_clocksource_read(vcpu_time);	/* time since system boot */
	delta += now.tv_sec * (u64)NSEC_PER_SEC + now.tv_nsec;

	now.tv_nsec = do_div(delta, NSEC_PER_SEC);
	now.tv_sec = delta;

	set_normalized_timespec(ts, now.tv_sec, now.tv_nsec);
}
Commit	Line	Data
7af192c9 GH	1	/* paravirtual clock -- common code used by kvm/xen
	2
	3	This program is free software; you can redistribute it and/or modify
	4	it under the terms of the GNU General Public License as published by
	5	the Free Software Foundation; either version 2 of the License, or
	6	(at your option) any later version.
	7
	8	This program is distributed in the hope that it will be useful,
	9	but WITHOUT ANY WARRANTY; without even the implied warranty of
	10	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	11	GNU General Public License for more details.
	12
	13	You should have received a copy of the GNU General Public License
	14	along with this program; if not, write to the Free Software
	15	Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
	16	*/
	17
	18	#include <linux/kernel.h>
	19	#include <linux/percpu.h>
	20	#include <asm/pvclock.h>
	21
	22	/*
	23	* These are perodically updated
	24	* xen: magic shared_info page
	25	* kvm: gpa registered via msr
	26	* and then copied here.
	27	*/
	28	struct pvclock_shadow_time {
	29	u64 tsc_timestamp; /* TSC at last update of time vals. */
	30	u64 system_timestamp; /* Time, in nanosecs, since boot. */
	31	u32 tsc_to_nsec_mul;
	32	int tsc_shift;
	33	u32 version;
424c32f1	34	u8 flags;
7af192c9 GH	35	};
7af192c9 GH	36
424c32f1 GC	37	static u8 valid_flags __read_mostly = 0;
	38
	39	void pvclock_set_flags(u8 flags)
	40	{
	41	valid_flags = flags;
	42	}
	43
7af192c9 GH	44	static u64 pvclock_get_nsec_offset(struct pvclock_shadow_time *shadow)
	45	{
	46	u64 delta = native_read_tsc() - shadow->tsc_timestamp;
347bb444 ZA	47	return pvclock_scale_delta(delta, shadow->tsc_to_nsec_mul,
347bb444 ZA	48	shadow->tsc_shift);
7af192c9 GH	49	}
	50
	51	/*
	52	* Reads a consistent set of time-base values from hypervisor,
	53	* into a shadow data area.
	54	*/
	55	static unsigned pvclock_get_time_values(struct pvclock_shadow_time *dst,
	56	struct pvclock_vcpu_time_info *src)
	57	{
	58	do {
	59	dst->version = src->version;
	60	rmb(); /* fetch version before data */
	61	dst->tsc_timestamp = src->tsc_timestamp;
	62	dst->system_timestamp = src->system_time;
	63	dst->tsc_to_nsec_mul = src->tsc_to_system_mul;
	64	dst->tsc_shift = src->tsc_shift;
424c32f1	65	dst->flags = src->flags;
7af192c9 GH	66	rmb(); /* test version after fetching data */
	67	} while ((src->version & 1) \|\| (dst->version != src->version));
	68
	69	return dst->version;
	70	}
	71
3807f345 GC	72	unsigned long pvclock_tsc_khz(struct pvclock_vcpu_time_info *src)
3807f345 GC	73	{
a0854600	74	u64 pv_tsc_khz = 1000000ULL << 32;
3807f345	75
a0854600	76	do_div(pv_tsc_khz, src->tsc_to_system_mul);
3807f345	77	if (src->tsc_shift < 0)
a0854600	78	pv_tsc_khz <<= -src->tsc_shift;
3807f345	79	else
a0854600 HH	80	pv_tsc_khz >>= src->tsc_shift;
a0854600 HH	81	return pv_tsc_khz;
3807f345 GC	82	}
3807f345 GC	83
489fb490 GC	84	static atomic64_t last_value = ATOMIC64_INIT(0);
489fb490 GC	85
7af192c9 GH	86	cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src)
	87	{
	88	struct pvclock_shadow_time shadow;
	89	unsigned version;
	90	cycle_t ret, offset;
489fb490	91	u64 last;
7af192c9 GH	92
	93	do {
	94	version = pvclock_get_time_values(&shadow, src);
	95	barrier();
	96	offset = pvclock_get_nsec_offset(&shadow);
	97	ret = shadow.system_timestamp + offset;
	98	barrier();
	99	} while (version != src->version);
	100
3a0d7256 GC	101	if ((valid_flags & PVCLOCK_TSC_STABLE_BIT) &&
	102	(shadow.flags & PVCLOCK_TSC_STABLE_BIT))
	103	return ret;
	104
489fb490 GC	105	/*
	106	* Assumption here is that last_value, a global accumulator, always goes
	107	* forward. If we are less than that, we should not be much smaller.
	108	* We assume there is an error marging we're inside, and then the correction
	109	* does not sacrifice accuracy.
	110	*
	111	* For reads: global may have changed between test and return,
	112	* but this means someone else updated poked the clock at a later time.
	113	* We just need to make sure we are not seeing a backwards event.
	114	*
	115	* For updates: last_value = ret is not enough, since two vcpus could be
	116	* updating at the same time, and one of them could be slightly behind,
	117	* making the assumption that last_value always go forward fail to hold.
	118	*/
	119	last = atomic64_read(&last_value);
	120	do {
	121	if (ret < last)
	122	return last;
	123	last = atomic64_cmpxchg(&last_value, last, ret);
	124	} while (unlikely(last != ret));
	125
7af192c9 GH	126	return ret;
	127	}
	128
	129	void pvclock_read_wallclock(struct pvclock_wall_clock *wall_clock,
	130	struct pvclock_vcpu_time_info *vcpu_time,
	131	struct timespec *ts)
	132	{
	133	u32 version;
	134	u64 delta;
	135	struct timespec now;
	136
	137	/* get wallclock at system boot */
	138	do {
	139	version = wall_clock->version;
	140	rmb(); /* fetch version before time */
	141	now.tv_sec = wall_clock->sec;
	142	now.tv_nsec = wall_clock->nsec;
	143	rmb(); /* fetch time before checking version */
	144	} while ((wall_clock->version & 1) \|\| (version != wall_clock->version));
	145
	146	delta = pvclock_clocksource_read(vcpu_time); /* time since system boot */
	147	delta += now.tv_sec * (u64)NSEC_PER_SEC + now.tv_nsec;
	148
	149	now.tv_nsec = do_div(delta, NSEC_PER_SEC);
	150	now.tv_sec = delta;
	151
	152	set_normalized_timespec(ts, now.tv_sec, now.tv_nsec);
	153	}