Reinstate cpu_est_clockrate() support for P-state invariant TSC if APERF and

MPERF MSRs are available.  It was disabled in r216443.  Remove the earlier
hack to subtract 0.5% from the calibrated frequency as DELAY(9) is little
bit more reliable now.

1 files changed, 24 insertions, 25 deletions

diff --git a/sys/i386/i386/machdep.c b/sys/i386/i386/machdep.c
index 5869c21..50ca5fd 100644
--- a/sys/i386/i386/machdep.c
+++ b/sys/i386/i386/machdep.c
@@ -1136,25 +1136,22 @@ cpu_flush_dcache(void *ptr, size_t len)
 int
 cpu_est_clockrate(int cpu_id, uint64_t *rate)
 {
+	uint64_t tsc1, tsc2;
+	uint64_t acnt, mcnt;
 	register_t reg;
-	uint64_t freq, tsc1, tsc2;
 
 	if (pcpu_find(cpu_id) == NULL || rate == NULL)
 		return (EINVAL);
 	if ((cpu_feature & CPUID_TSC) == 0)
 		return (EOPNOTSUPP);
-	freq = atomic_load_acq_64(&tsc_freq);
 
-	/* If TSC is P-state invariant, DELAY(9) based logic fails. */
-	if (tsc_is_invariant && freq != 0)
+	/*
+	 * If TSC is P-state invariant and APERF/MPERF MSRs do not exist,
+	 * DELAY(9) based logic fails.
+	 */
+	if (tsc_is_invariant && !tsc_perf_stat)
 		return (EOPNOTSUPP);
 
-	/* If we're booting, trust the rate calibrated moments ago. */
-	if (cold && freq != 0) {
-		*rate = freq;
-		return (0);
-	}
-
 #ifdef SMP
 	if (smp_cpus > 1) {
 		/* Schedule ourselves on the indicated cpu. */
@@ -1166,10 +1163,23 @@ cpu_est_clockrate(int cpu_id, uint64_t *rate)
 
 	/* Calibrate by measuring a short delay. */
 	reg = intr_disable();
-	tsc1 = rdtsc();
-	DELAY(1000);
-	tsc2 = rdtsc();
-	intr_restore(reg);
+	if (tsc_is_invariant) {
+		wrmsr(MSR_MPERF, 0);
+		wrmsr(MSR_APERF, 0);
+		tsc1 = rdtsc();
+		DELAY(1000);
+		mcnt = rdmsr(MSR_MPERF);
+		acnt = rdmsr(MSR_APERF);
+		tsc2 = rdtsc();
+		intr_restore(reg);
+		*rate = (tsc2 - tsc1) / 1000 * acnt / mcnt * 1000000;
+	} else {
+		tsc1 = rdtsc();
+		DELAY(1000);
+		tsc2 = rdtsc();
+		intr_restore(reg);
+		*rate = (tsc2 - tsc1) * 1000;
+	}
 
 #ifdef SMP
 	if (smp_cpus > 1) {
@@ -1179,17 +1189,6 @@ cpu_est_clockrate(int cpu_id, uint64_t *rate)
 	}
 #endif
 
-	tsc2 -= tsc1;
-	if (freq != 0) {
-		*rate = tsc2 * 1000;
-		return (0);
-	}
-
-	/*
-	 * Subtract 0.5% of the total.  Empirical testing has shown that
-	 * overhead in DELAY() works out to approximately this value.
-	 */
-	*rate = tsc2 * 1000 - tsc2 * 5;
 	return (0);
 }