Add a tunable "machdep.disable_tsc" to turn off TSC. Specifically, it turns

off boot-time CPU frequency calibration, DELAY(9) with TSC, and using TSC as
a CPU ticker.  Note tsc_present does not change by this tunable.

5 files changed, 71 insertions, 36 deletions

diff --git a/sys/amd64/amd64/machdep.c b/sys/amd64/amd64/machdep.c
index 0bb552c..808dc08 100644
--- a/sys/amd64/amd64/machdep.c
+++ b/sys/amd64/amd64/machdep.c
@@ -80,6 +80,9 @@ __FBSDID("$FreeBSD$");
 #include <sys/reboot.h>
 #include <sys/sched.h>
 #include <sys/signalvar.h>
+#ifdef SMP
+#include <sys/smp.h>
+#endif
 #include <sys/syscallsubr.h>
 #include <sys/sysctl.h>
 #include <sys/sysent.h>
@@ -544,20 +547,22 @@ cpu_est_clockrate(int cpu_id, uint64_t *rate)
 		return (EINVAL);
 
 	/* If TSC is P-state invariant, DELAY(9) based logic fails. */
-	if (tsc_is_invariant)
+	if (tsc_is_invariant && tsc_freq != 0)
 		return (EOPNOTSUPP);
 
 	/* If we're booting, trust the rate calibrated moments ago. */
-	if (cold) {
+	if (cold && tsc_freq != 0) {
 		*rate = tsc_freq;
 		return (0);
 	}
 
 #ifdef SMP
-	/* Schedule ourselves on the indicated cpu. */
-	thread_lock(curthread);
-	sched_bind(curthread, cpu_id);
-	thread_unlock(curthread);
+	if (smp_cpus > 1) {
+		/* Schedule ourselves on the indicated cpu. */
+		thread_lock(curthread);
+		sched_bind(curthread, cpu_id);
+		thread_unlock(curthread);
+	}
 #endif
 
 	/* Calibrate by measuring a short delay. */
@@ -568,12 +573,24 @@ cpu_est_clockrate(int cpu_id, uint64_t *rate)
 	intr_restore(reg);
 
 #ifdef SMP
-	thread_lock(curthread);
-	sched_unbind(curthread);
-	thread_unlock(curthread);
+	if (smp_cpus > 1) {
+		thread_lock(curthread);
+		sched_unbind(curthread);
+		thread_unlock(curthread);
+	}
 #endif
 
-	*rate = (tsc2 - tsc1) * 1000;
+	tsc2 -= tsc1;
+	if (tsc_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);
 }
 
diff --git a/sys/contrib/altq/altq/altq_subr.c b/sys/contrib/altq/altq/altq_subr.c
index 7d2fc77..a58747d 100644
--- a/sys/contrib/altq/altq/altq_subr.c
+++ b/sys/contrib/altq/altq/altq_subr.c
@@ -78,10 +78,10 @@
 #include <machine/clock.h>
 #endif
 #if defined(__amd64__) || defined(__i386__)
+#include <machine/cpu.h>		/* for cpu_feature or tsc_present */
 #include <machine/cpufunc.h>		/* for pentium tsc */
 #if defined(__NetBSD__) || defined(__OpenBSD__)
 #include <machine/specialreg.h>		/* for CPUID_TSC */
-#include <machine/cpu.h>		/* for cpu_feature */
 #endif
 #endif /* __amd64 || __i386__ */
 
@@ -927,7 +927,7 @@ init_machclk_setup(void)
 #if defined(__amd64__) || defined(__i386__)
 	/* check if TSC is available */
 #ifdef __FreeBSD__
-	if (tsc_freq == 0)
+	if (!tsc_present || tsc_freq == 0)
 #else
 	if ((cpu_feature & CPUID_TSC) == 0)
 #endif
diff --git a/sys/i386/i386/machdep.c b/sys/i386/i386/machdep.c
index c5c0dfc..a87095f 100644
--- a/sys/i386/i386/machdep.c
+++ b/sys/i386/i386/machdep.c
@@ -79,6 +79,9 @@ __FBSDID("$FreeBSD$");
 #include <sys/reboot.h>
 #include <sys/sched.h>
 #include <sys/signalvar.h>
+#ifdef SMP
+#include <sys/smp.h>
+#endif
 #include <sys/syscallsubr.h>
 #include <sys/sysctl.h>
 #include <sys/sysent.h>
@@ -1142,20 +1145,22 @@ cpu_est_clockrate(int cpu_id, uint64_t *rate)
 		return (EOPNOTSUPP);
 
 	/* If TSC is P-state invariant, DELAY(9) based logic fails. */
-	if (tsc_is_invariant)
+	if (tsc_is_invariant && tsc_freq != 0)
 		return (EOPNOTSUPP);
 
 	/* If we're booting, trust the rate calibrated moments ago. */
-	if (cold) {
+	if (cold && tsc_freq != 0) {
 		*rate = tsc_freq;
 		return (0);
 	}
 
 #ifdef SMP
-	/* Schedule ourselves on the indicated cpu. */
-	thread_lock(curthread);
-	sched_bind(curthread, cpu_id);
-	thread_unlock(curthread);
+	if (smp_cpus > 1) {
+		/* Schedule ourselves on the indicated cpu. */
+		thread_lock(curthread);
+		sched_bind(curthread, cpu_id);
+		thread_unlock(curthread);
+	}
 #endif
 
 	/* Calibrate by measuring a short delay. */
@@ -1166,9 +1171,11 @@ cpu_est_clockrate(int cpu_id, uint64_t *rate)
 	intr_restore(reg);
 
 #ifdef SMP
-	thread_lock(curthread);
-	sched_unbind(curthread);
-	thread_unlock(curthread);
+	if (smp_cpus > 1) {
+		thread_lock(curthread);
+		sched_unbind(curthread);
+		thread_unlock(curthread);
+	}
 #endif
 
 	tsc2 -= tsc1;
diff --git a/sys/pc98/pc98/machdep.c b/sys/pc98/pc98/machdep.c
index 07b3b84..c1d065c 100644
--- a/sys/pc98/pc98/machdep.c
+++ b/sys/pc98/pc98/machdep.c
@@ -77,6 +77,9 @@ __FBSDID("$FreeBSD$");
 #include <sys/reboot.h>
 #include <sys/sched.h>
 #include <sys/signalvar.h>
+#ifdef SMP
+#include <sys/smp.h>
+#endif
 #include <sys/syscallsubr.h>
 #include <sys/sysctl.h>
 #include <sys/sysent.h>
@@ -1077,16 +1080,18 @@ cpu_est_clockrate(int cpu_id, uint64_t *rate)
 		return (EOPNOTSUPP);
 
 	/* If we're booting, trust the rate calibrated moments ago. */
-	if (cold) {
+	if (cold && tsc_freq != 0) {
 		*rate = tsc_freq;
 		return (0);
 	}
 
 #ifdef SMP
-	/* Schedule ourselves on the indicated cpu. */
-	thread_lock(curthread);
-	sched_bind(curthread, cpu_id);
-	thread_unlock(curthread);
+	if (smp_cpus > 1) {
+		/* Schedule ourselves on the indicated cpu. */
+		thread_lock(curthread);
+		sched_bind(curthread, cpu_id);
+		thread_unlock(curthread);
+	}
 #endif
 
 	/* Calibrate by measuring a short delay. */
@@ -1097,9 +1102,11 @@ cpu_est_clockrate(int cpu_id, uint64_t *rate)
 	intr_restore(reg);
 
 #ifdef SMP
-	thread_lock(curthread);
-	sched_unbind(curthread);
-	thread_unlock(curthread);
+	if (smp_cpus > 1) {
+		thread_lock(curthread);
+		sched_unbind(curthread);
+		thread_unlock(curthread);
+	}
 #endif
 
 	tsc2 -= tsc1;
diff --git a/sys/x86/x86/tsc.c b/sys/x86/x86/tsc.c
index 3e0300b..40d5f3c 100644
--- a/sys/x86/x86/tsc.c
+++ b/sys/x86/x86/tsc.c
@@ -63,6 +63,11 @@ SYSCTL_INT(_kern_timecounter, OID_AUTO, smp_tsc, CTLFLAG_RDTUN, &smp_tsc, 0,
 TUNABLE_INT("kern.timecounter.smp_tsc", &smp_tsc);
 #endif
 
+static int	tsc_disabled;
+SYSCTL_INT(_machdep, OID_AUTO, disable_tsc, CTLFLAG_RDTUN, &tsc_disabled, 0,
+    "Disable x86 Time Stamp Counter");
+TUNABLE_INT("machdep.disable_tsc", &tsc_disabled);
+
 static void tsc_freq_changed(void *arg, const struct cf_level *level,
     int status);
 static void tsc_freq_changing(void *arg, const struct cf_level *level,
@@ -84,12 +89,11 @@ init_TSC(void)
 {
 	u_int64_t tscval[2];
 
-	if (cpu_feature & CPUID_TSC)
-		tsc_present = 1;
-	else
-		tsc_present = 0;
+	if ((cpu_feature & CPUID_TSC) == 0)
+		return;
+	tsc_present = 1;
 
-	if (!tsc_present) 
+	if (tsc_disabled)
 		return;
 
 	if (bootverbose)
@@ -151,7 +155,7 @@ void
 init_TSC_tc(void)
 {
 
-	if (!tsc_present) 
+	if (!tsc_present || tsc_disabled)
 		return;
 
 	/*
@@ -248,7 +252,7 @@ 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 (tsc_disabled || status != 0)
 		return;
 
 	/* Total setting for this level gives the new frequency in MHz. */