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
);