1 /* paravirtual clock -- common code used by kvm/xen
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.
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.
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
18 #include <linux/kernel.h>
19 #include <linux/percpu.h>
20 #include <asm/pvclock.h>
22 static u8 valid_flags __read_mostly = 0;
24 void pvclock_set_flags(u8 flags)
29 static u64 pvclock_get_nsec_offset(const struct pvclock_vcpu_time_info *src)
31 u64 delta = native_read_tsc() - src->tsc_timestamp;
32 return pvclock_scale_delta(delta, src->tsc_to_system_mul,
36 unsigned long pvclock_tsc_khz(struct pvclock_vcpu_time_info *src)
38 u64 pv_tsc_khz = 1000000ULL << 32;
40 do_div(pv_tsc_khz, src->tsc_to_system_mul);
41 if (src->tsc_shift < 0)
42 pv_tsc_khz <<= -src->tsc_shift;
44 pv_tsc_khz >>= src->tsc_shift;
48 static atomic64_t last_value = ATOMIC64_INIT(0);
50 void pvclock_resume(void)
52 atomic64_set(&last_value, 0);
55 cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src)
63 version = src->version;
65 offset = pvclock_get_nsec_offset(src);
66 ret = src->system_time + offset;
69 } while ((src->version & 1) || version != src->version);
71 if ((valid_flags & PVCLOCK_TSC_STABLE_BIT) &&
72 (flags & PVCLOCK_TSC_STABLE_BIT))
76 * Assumption here is that last_value, a global accumulator, always goes
77 * forward. If we are less than that, we should not be much smaller.
78 * We assume there is an error marging we're inside, and then the correction
79 * does not sacrifice accuracy.
81 * For reads: global may have changed between test and return,
82 * but this means someone else updated poked the clock at a later time.
83 * We just need to make sure we are not seeing a backwards event.
85 * For updates: last_value = ret is not enough, since two vcpus could be
86 * updating at the same time, and one of them could be slightly behind,
87 * making the assumption that last_value always go forward fail to hold.
89 last = atomic64_read(&last_value);
93 last = atomic64_cmpxchg(&last_value, last, ret);
94 } while (unlikely(last != ret));
99 void pvclock_read_wallclock(struct pvclock_wall_clock *wall_clock,
100 struct pvclock_vcpu_time_info *vcpu_time,
107 /* get wallclock at system boot */
109 version = wall_clock->version;
110 rmb(); /* fetch version before time */
111 now.tv_sec = wall_clock->sec;
112 now.tv_nsec = wall_clock->nsec;
113 rmb(); /* fetch time before checking version */
114 } while ((wall_clock->version & 1) || (version != wall_clock->version));
116 delta = pvclock_clocksource_read(vcpu_time); /* time since system boot */
117 delta += now.tv_sec * (u64)NSEC_PER_SEC + now.tv_nsec;
119 now.tv_nsec = do_div(delta, NSEC_PER_SEC);
122 set_normalized_timespec(ts, now.tv_sec, now.tv_nsec);