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.
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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 unsigned long pvclock_tsc_khz(struct pvclock_vcpu_time_info *src)
31 u64 pv_tsc_khz = 1000000ULL << 32;
33 do_div(pv_tsc_khz, src->tsc_to_system_mul);
34 if (src->tsc_shift < 0)
35 pv_tsc_khz <<= -src->tsc_shift;
37 pv_tsc_khz >>= src->tsc_shift;
41 static atomic64_t last_value = ATOMIC64_INIT(0);
43 void pvclock_resume(void)
45 atomic64_set(&last_value, 0);
48 cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src)
56 version = __pvclock_read_cycles(src, &ret, &flags);
57 } while ((src->version & 1) || version != src->version);
59 if ((valid_flags & PVCLOCK_TSC_STABLE_BIT) &&
60 (flags & PVCLOCK_TSC_STABLE_BIT))
64 * Assumption here is that last_value, a global accumulator, always goes
65 * forward. If we are less than that, we should not be much smaller.
66 * We assume there is an error marging we're inside, and then the correction
67 * does not sacrifice accuracy.
69 * For reads: global may have changed between test and return,
70 * but this means someone else updated poked the clock at a later time.
71 * We just need to make sure we are not seeing a backwards event.
73 * For updates: last_value = ret is not enough, since two vcpus could be
74 * updating at the same time, and one of them could be slightly behind,
75 * making the assumption that last_value always go forward fail to hold.
77 last = atomic64_read(&last_value);
81 last = atomic64_cmpxchg(&last_value, last, ret);
82 } while (unlikely(last != ret));
87 void pvclock_read_wallclock(struct pvclock_wall_clock *wall_clock,
88 struct pvclock_vcpu_time_info *vcpu_time,
95 /* get wallclock at system boot */
97 version = wall_clock->version;
98 rmb(); /* fetch version before time */
99 now.tv_sec = wall_clock->sec;
100 now.tv_nsec = wall_clock->nsec;
101 rmb(); /* fetch time before checking version */
102 } while ((wall_clock->version & 1) || (version != wall_clock->version));
104 delta = pvclock_clocksource_read(vcpu_time); /* time since system boot */
105 delta += now.tv_sec * (u64)NSEC_PER_SEC + now.tv_nsec;
107 now.tv_nsec = do_div(delta, NSEC_PER_SEC);
110 set_normalized_timespec(ts, now.tv_sec, now.tv_nsec);