Gerd Hoffmann wrote:
> Wall clock is off a few hours though. Oops.
>
> I think the way wall clock and system clock work together in xen (Jeremy
> correct me if I'm wrong) is that the wall clock specifies the point in
> time where the system clock started going. As kvm fills in host system
> time into the guest system time fields the guest wall clock fields
> should be filled with the host boot time timestamp I'd say.
Following up myself with a quick&dirty patch to tackle this issue too.
This one calculates the boot time. That should be solveable better,
include/linux/time.h lists two functions which sound promising:
extern void getboottime(struct timespec *ts);
extern void monotonic_to_bootbased(struct timespec *ts);
Neither of them is available to modules though, so I can't test without
rebooting my laptop ...
monotonic_to_bootbased() sounds like we would get hosts ntp adjustments
in the guests for free.
cheers,
Gerd
--
http://kraxel.fedorapeople.org/xenner/
diff -up kvm-65/kernel/x86.c.fix kvm-65/kernel/x86.c
--- kvm-65/kernel/x86.c.fix 2008-04-06 21:23:07.000000000 +0200
+++ kvm-65/kernel/x86.c 2008-04-11 16:17:23.000000000 +0200
@@ -490,7 +490,7 @@ static void kvm_write_wall_clock(struct
{
static int version;
struct kvm_wall_clock wc;
- struct timespec wc_ts;
+ struct timespec now,sys,boot;
if (!wall_clock)
return;
@@ -499,9 +499,11 @@ static void kvm_write_wall_clock(struct
kvm_write_guest(kvm, wall_clock, &version, sizeof(version));
- wc_ts = current_kernel_time();
- wc.wc_sec = wc_ts.tv_sec;
- wc.wc_nsec = wc_ts.tv_nsec;
+ now = current_kernel_time();
+ ktime_get_ts(&sys);
+ boot = ns_to_timespec(timespec_to_ns(&now) - timespec_to_ns(&sys));
+ wc.wc_sec = boot.tv_sec;
+ wc.wc_nsec = boot.tv_nsec;
wc.wc_version = version;
kvm_write_guest(kvm, wall_clock, &wc, sizeof(wc));
@@ -548,6 +550,44 @@ static void kvm_write_guest_time(struct
mark_page_dirty(v->kvm, vcpu->time >> PAGE_SHIFT);
}
+static uint32_t div_frac(uint32_t dividend, uint32_t divisor)
+{
+ uint32_t quotient, remainder;
+
+ __asm__ ( "divl %4"
+ : "=a" (quotient), "=d" (remainder)
+ : "0" (0), "1" (dividend), "r" (divisor) );
+ return quotient;
+}
+
+static void kvm_set_time_scale(uint32_t tsc_khz, struct kvm_vcpu_time_info *hv_clock)
+{
+ uint64_t nsecs = 1000000000LL;
+ int32_t shift = 0;
+ uint64_t tps64;
+ uint32_t tps32;
+
+ tps64 = tsc_khz * 1000LL;
+ while (tps64 > nsecs*2) {
+ tps64 >>= 1;
+ shift--;
+ }
+
+ tps32 = (uint32_t)tps64;
+ while (tps32 <= (uint32_t)nsecs) {
+ tps32 <<= 1;
+ shift++;
+ }
+
+ hv_clock->tsc_shift = shift;
+ hv_clock->tsc_to_system_mul = div_frac(nsecs, tps32);
+
+#if 0
+ printk(KERN_DEBUG "%s: tsc_khz %u, tsc_shift %d, tsc_mul %u\n",
+ __FUNCTION__, tsc_khz, hv_clock->tsc_shift,
+ hv_clock->tsc_to_system_mul);
+#endif
+}
int kvm_set_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 data)
{
@@ -596,9 +636,7 @@ int kvm_set_msr_common(struct kvm_vcpu *
/* ...but clean it before doing the actual write */
vcpu->arch.time_offset = data & ~(PAGE_MASK | 1);
- vcpu->arch.hv_clock.tsc_to_system_mul =
- clocksource_khz2mult(kvm_tsc_khz, 22);
- vcpu->arch.hv_clock.tsc_shift = 22;
+ kvm_set_time_scale(kvm_tsc_khz, &vcpu->arch.hv_clock);
down_read(¤t->mm->mmap_sem);
vcpu->arch.time_page =
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