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>
23 * These are perodically updated
24 * xen: magic shared_info page
25 * kvm: gpa registered via msr
26 * and then copied here.
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. */
37 static u8 valid_flags __read_mostly = 0;
39 void pvclock_set_flags(u8 flags)
45 * Scale a 64-bit delta by scaling and multiplying by a 32-bit fraction,
46 * yielding a 64-bit result.
48 static inline u64 scale_delta(u64 delta, u32 mul_frac, int shift)
69 : "=A" (product), "=r" (tmp1), "=r" (tmp2)
70 : "a" ((u32)delta), "1" ((u32)(delta >> 32)), "2" (mul_frac) );
71 #elif defined(__x86_64__)
73 "mul %%rdx ; shrd $32,%%rdx,%%rax"
74 : "=a" (product) : "0" (delta), "d" ((u64)mul_frac) );
82 static u64 pvclock_get_nsec_offset(struct pvclock_shadow_time *shadow)
84 u64 delta = native_read_tsc() - shadow->tsc_timestamp;
85 return scale_delta(delta, shadow->tsc_to_nsec_mul, shadow->tsc_shift);
89 * Reads a consistent set of time-base values from hypervisor,
90 * into a shadow data area.
92 static unsigned pvclock_get_time_values(struct pvclock_shadow_time *dst,
93 struct pvclock_vcpu_time_info *src)
96 dst->version = src->version;
97 rmb(); /* fetch version before data */
98 dst->tsc_timestamp = src->tsc_timestamp;
99 dst->system_timestamp = src->system_time;
100 dst->tsc_to_nsec_mul = src->tsc_to_system_mul;
101 dst->tsc_shift = src->tsc_shift;
102 dst->flags = src->flags;
103 rmb(); /* test version after fetching data */
104 } while ((src->version & 1) || (dst->version != src->version));
109 unsigned long pvclock_tsc_khz(struct pvclock_vcpu_time_info *src)
111 u64 pv_tsc_khz = 1000000ULL << 32;
113 do_div(pv_tsc_khz, src->tsc_to_system_mul);
114 if (src->tsc_shift < 0)
115 pv_tsc_khz <<= -src->tsc_shift;
117 pv_tsc_khz >>= src->tsc_shift;
121 static atomic64_t last_value = ATOMIC64_INIT(0);
123 cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src)
125 struct pvclock_shadow_time shadow;
131 version = pvclock_get_time_values(&shadow, src);
133 offset = pvclock_get_nsec_offset(&shadow);
134 ret = shadow.system_timestamp + offset;
136 } while (version != src->version);
138 if ((valid_flags & PVCLOCK_TSC_STABLE_BIT) &&
139 (shadow.flags & PVCLOCK_TSC_STABLE_BIT))
143 * Assumption here is that last_value, a global accumulator, always goes
144 * forward. If we are less than that, we should not be much smaller.
145 * We assume there is an error marging we're inside, and then the correction
146 * does not sacrifice accuracy.
148 * For reads: global may have changed between test and return,
149 * but this means someone else updated poked the clock at a later time.
150 * We just need to make sure we are not seeing a backwards event.
152 * For updates: last_value = ret is not enough, since two vcpus could be
153 * updating at the same time, and one of them could be slightly behind,
154 * making the assumption that last_value always go forward fail to hold.
156 last = atomic64_read(&last_value);
160 last = atomic64_cmpxchg(&last_value, last, ret);
161 } while (unlikely(last != ret));
166 void pvclock_read_wallclock(struct pvclock_wall_clock *wall_clock,
167 struct pvclock_vcpu_time_info *vcpu_time,
174 /* get wallclock at system boot */
176 version = wall_clock->version;
177 rmb(); /* fetch version before time */
178 now.tv_sec = wall_clock->sec;
179 now.tv_nsec = wall_clock->nsec;
180 rmb(); /* fetch time before checking version */
181 } while ((wall_clock->version & 1) || (version != wall_clock->version));
183 delta = pvclock_clocksource_read(vcpu_time); /* time since system boot */
184 delta += now.tv_sec * (u64)NSEC_PER_SEC + now.tv_nsec;
186 now.tv_nsec = do_div(delta, NSEC_PER_SEC);
189 set_normalized_timespec(ts, now.tv_sec, now.tv_nsec);