svn commit: r225069 - head/sys/x86/x86

Mike Silbersack silby at FreeBSD.org
Mon Aug 22 03:10:30 UTC 2011


Author: silby
Date: Mon Aug 22 03:10:29 2011
New Revision: 225069
URL: http://svn.freebsd.org/changeset/base/225069

Log:
  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

Modified:
  head/sys/x86/x86/tsc.c

Modified: head/sys/x86/x86/tsc.c
==============================================================================
--- head/sys/x86/x86/tsc.c	Sun Aug 21 22:09:30 2011	(r225068)
+++ head/sys/x86/x86/tsc.c	Mon Aug 22 03:10:29 2011	(r225069)
@@ -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)


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