Use atomic load & store for TSC frequency. It may be overkill for amd64 but

safer for i386 because it can be easily over 4 GHz now.  More worse, it can
be easily changed by user with 'machdep.tsc_freq' tunable (directly) or
cpufreq(4) (indirectly).  Note it is intentionally not used in performance
critical paths to avoid performance regression (but we should, in theory).
Alternatively, we may add "virtual TSC" with lower frequency if maximum
frequency overflows 32 bits (and ignore possible incoherency as we do now).

1 files changed, 17 insertions, 11 deletions

diff --git a/sys/i386/isa/prof_machdep.c b/sys/i386/isa/prof_machdep.c
index adeddf2..bdcd7e4 100644
--- a/sys/i386/isa/prof_machdep.c
+++ b/sys/i386/isa/prof_machdep.c
@@ -170,8 +170,8 @@ cputime()
 {
 	u_int count;
 	int delta;
-#if (defined(I586_CPU) || defined(I686_CPU)) && !defined(SMP) && \
-    defined(PERFMON) && defined(I586_PMC_GUPROF)
+#if (defined(I586_CPU) || defined(I686_CPU)) && \
+    defined(PERFMON) && defined(I586_PMC_GUPROF) && !defined(SMP)
 	u_quad_t event_count;
 #endif
 	u_char high, low;
@@ -286,21 +286,23 @@ void
 startguprof(gp)
 	struct gmonparam *gp;
 {
-	if (cputime_clock == CPUTIME_CLOCK_UNINITIALIZED) {
-		cputime_clock = CPUTIME_CLOCK_I8254;
 #if defined(I586_CPU) || defined(I686_CPU)
-		if (tsc_freq != 0 && mp_ncpus == 1)
+	uint64_t freq;
+
+	freq = atomic_load_acq_64(&tsc_freq);
+	if (cputime_clock == CPUTIME_CLOCK_UNINITIALIZED) {
+		if (freq != 0 && mp_ncpus == 1)
 			cputime_clock = CPUTIME_CLOCK_TSC;
-#endif
+		else
+			cputime_clock = CPUTIME_CLOCK_I8254;
 	}
-	gp->profrate = i8254_freq << CPUTIME_CLOCK_I8254_SHIFT;
-#if defined(I586_CPU) || defined(I686_CPU)
 	if (cputime_clock == CPUTIME_CLOCK_TSC) {
-		gp->profrate = tsc_freq >> 1;
+		gp->profrate = freq >> 1;
 		cputime_prof_active = 1;
-	}
+	} else
+		gp->profrate = i8254_freq << CPUTIME_CLOCK_I8254_SHIFT;
 #if defined(PERFMON) && defined(I586_PMC_GUPROF)
-	else if (cputime_clock == CPUTIME_CLOCK_I586_PMC) {
+	if (cputime_clock == CPUTIME_CLOCK_I586_PMC) {
 		if (perfmon_avail() &&
 		    perfmon_setup(0, cputime_clock_pmc_conf) == 0) {
 			if (perfmon_start(0) != 0)
@@ -325,6 +327,10 @@ startguprof(gp)
 		}
 	}
 #endif /* PERFMON && I586_PMC_GUPROF */
+#else /* !(I586_CPU || I686_CPU) */
+	if (cputime_clock == CPUTIME_CLOCK_UNINITIALIZED)
+		cputime_clock = CPUTIME_CLOCK_I8254;
+	gp->profrate = i8254_freq << CPUTIME_CLOCK_I8254_SHIFT;
 #endif /* I586_CPU || I686_CPU */
 	cputime_bias = 0;
 	cputime();