Add interface to derive a TSC frequency from the pvclock

This can later use this to determine the TSC frequency like is done with
VMware, instead of using a DELAY loop that is not always accurate in an VM.

MFC after:	1 month

2 files changed, 16 insertions, 0 deletions

diff --git a/sys/x86/include/pvclock.h b/sys/x86/include/pvclock.h
index 88a596f..402ffed 100644
--- a/sys/x86/include/pvclock.h
+++ b/sys/x86/include/pvclock.h
@@ -51,6 +51,7 @@ struct pvclock_wall_clock {
 
 void		pvclock_resume(void);
 uint64_t	pvclock_get_last_cycles(void);
+uint64_t	pvclock_tsc_freq(struct pvclock_vcpu_time_info *ti);
 uint64_t	pvclock_get_timecount(struct pvclock_vcpu_time_info *ti);
 void		pvclock_get_wallclock(struct pvclock_wall_clock *wc,
 		    struct timespec *ts);
diff --git a/sys/x86/x86/pvclock.c b/sys/x86/x86/pvclock.c
index ebc37a4..c1e6f83 100644
--- a/sys/x86/x86/pvclock.c
+++ b/sys/x86/x86/pvclock.c
@@ -58,6 +58,21 @@ pvclock_get_last_cycles(void)
 	return (atomic_load_acq_64(&pvclock_last_cycles));
 }
 
+uint64_t
+pvclock_tsc_freq(struct pvclock_vcpu_time_info *ti)
+{
+	uint64_t freq;
+
+	freq = (1000000000ULL << 32) / ti->tsc_to_system_mul;
+
+	if (ti->tsc_shift < 0)
+		freq <<= -ti->tsc_shift;
+	else
+		freq >>= ti->tsc_shift;
+
+	return (freq);
+}
+
 /*
  * Scale a 64-bit delta by scaling and multiplying by a 32-bit fraction,
  * yielding a 64-bit result.