Turn off CPU frequency change notifiers when the TSC is P-state invariant

or it is forced by setting 'kern.timecounter.invariant_tsc' tunable
to non-zero.

4 files changed, 30 insertions, 8 deletions

diff --git a/sys/amd64/amd64/identcpu.c b/sys/amd64/amd64/identcpu.c
index 30ab367..5d5f401 100644
--- a/sys/amd64/amd64/identcpu.c
+++ b/sys/amd64/amd64/identcpu.c
@@ -347,6 +347,12 @@ printcpuinfo(void)
 			    "AuthenticAMD") == 0)
 				cpu_feature &= ~CPUID_HTT;
 
+			if (!tsc_is_invariant &&
+			    (amd_pminfo & AMDPM_TSC_INVARIANT)) {
+				tsc_is_invariant = 1;
+				printf("\n  P-state invariant TSC");
+			}
+
 			/*
 			 * If this CPU supports HTT or CMP then mention the
 			 * number of physical/logical cores it contains.
@@ -409,8 +415,11 @@ panicifcpuunsupported(void)
 static void
 tsc_freq_changed(void *arg, const struct cf_level *level, int status)
 {
-	/* If there was an error during the transition, don't do anything. */
-	if (status != 0)
+	/*
+	 * If there was an error during the transition or
+	 * TSC is P-state invariant, don't do anything.
+	 */
+	if (status != 0 || tsc_is_invariant)
 		return;
 
 	/* Total setting for this level gives the new frequency in MHz. */
diff --git a/sys/amd64/amd64/prof_machdep.c b/sys/amd64/amd64/prof_machdep.c
index dad52df..6c848df 100644
--- a/sys/amd64/amd64/prof_machdep.c
+++ b/sys/amd64/amd64/prof_machdep.c
@@ -383,8 +383,11 @@ static void
 tsc_freq_changed(void *arg, const struct cf_level *level, int status)
 {
 
-	/* If there was an error during the transition, don't do anything. */
-	if (status != 0)
+	/*
+	 * If there was an error during the transition or
+	 * TSC is P-state invariant, don't do anything.
+	 */
+	if (status != 0 || tsc_is_invariant)
 		return;
 	if (cputime_prof_active && cputime_clock == CPUTIME_CLOCK_TSC)
 		printf("warning: cpu freq changed while profiling active\n");
diff --git a/sys/amd64/amd64/tsc.c b/sys/amd64/amd64/tsc.c
index 3c66a33..dcda751 100644
--- a/sys/amd64/amd64/tsc.c
+++ b/sys/amd64/amd64/tsc.c
@@ -48,8 +48,13 @@ __FBSDID("$FreeBSD$");
 
 uint64_t	tsc_freq;
 int		tsc_is_broken;
+int		tsc_is_invariant;
 static eventhandler_tag tsc_levels_tag, tsc_pre_tag, tsc_post_tag;
 
+SYSCTL_INT(_kern_timecounter, OID_AUTO, invariant_tsc, CTLFLAG_RDTUN,
+    &tsc_is_invariant, 0, "Indicates whether the TSC is P-state invariant");
+TUNABLE_INT("kern.timecounter.invariant_tsc", &tsc_is_invariant);
+
 #ifdef SMP
 static int	smp_tsc;
 SYSCTL_INT(_kern_timecounter, OID_AUTO, smp_tsc, CTLFLAG_RDTUN, &smp_tsc, 0,
@@ -174,11 +179,12 @@ static void
 tsc_freq_changing(void *arg, const struct cf_level *level, int *status)
 {
 
-	if (*status != 0 || timecounter != &tsc_timecounter)
+	if (*status != 0 || timecounter != &tsc_timecounter ||
+	    tsc_is_invariant)
 		return;
 
 	printf("timecounter TSC must not be in use when "
-	     "changing frequencies; change denied\n");
+	    "changing frequencies; change denied\n");
 	*status = EBUSY;
 }
 
@@ -186,8 +192,11 @@ tsc_freq_changing(void *arg, const struct cf_level *level, int *status)
 static void
 tsc_freq_changed(void *arg, const struct cf_level *level, int status)
 {
-	/* If there was an error during the transition, don't do anything. */
-	if (status != 0)
+	/*
+	 * If there was an error during the transition or
+	 * TSC is P-state invariant, don't do anything.
+	 */
+	if (status != 0 || tsc_is_invariant)
 		return;
 
 	/* Total setting for this level gives the new frequency in MHz. */
diff --git a/sys/amd64/include/clock.h b/sys/amd64/include/clock.h
index de09de3..f8745f9c 100644
--- a/sys/amd64/include/clock.h
+++ b/sys/amd64/include/clock.h
@@ -20,6 +20,7 @@ extern u_int	i8254_freq;
 extern int	i8254_max_count;
 extern uint64_t	tsc_freq;
 extern int	tsc_is_broken;
+extern int	tsc_is_invariant;
 
 void	i8254_init(void);