Disable TSC usage inside SMP VM environments. On my VMware ESXi 4.1

environment with a core i5-2500K, operation in this mode causes timeouts
from the mpt driver.  Switching to the ACPI-fast timer resolves this issue.
Switching the VM back to single CPU mode also works, which is why I have
not disabled the TSC in that mode.

I did not test with KVM or other VM environments, but I am being cautious
and assuming that the TSC is not reliable in SMP mode there as well.

Reviewed by:	kib
Approved by:	re (kib)
MFC after:	Not applicable, the timecounter code is new for 9.x

1 files changed, 8 insertions, 3 deletions

diff --git a/sys/x86/x86/tsc.c b/sys/x86/x86/tsc.c
index 0b383bf..4d1618f 100644
--- a/sys/x86/x86/tsc.c
+++ b/sys/x86/x86/tsc.c
@@ -464,11 +464,16 @@ init_TSC_tc(void)
 	 * synchronized.  If the user is sure that the system has synchronized
 	 * TSCs, set kern.timecounter.smp_tsc tunable to a non-zero value.
 	 * We also limit the frequency even lower to avoid "temporal anomalies"
-	 * as much as possible.
+	 * as much as possible.  The TSC seems unreliable in virtualized SMP
+	 * environments, so it is set to a negative quality in those cases.
 	 */
 	if (smp_cpus > 1) {
-		tsc_timecounter.tc_quality = test_smp_tsc();
-		max_freq >>= 8;
+		if (vm_guest != 0) {
+			tsc_timecounter.tc_quality = -100;
+		} else {
+			tsc_timecounter.tc_quality = test_smp_tsc();
+			max_freq >>= 8;
+		}
 	} else
 #endif
 	if (tsc_is_invariant)