svn commit: r345359 - in head/sys/cddl/dev/dtrace: amd64 i386

[Mark Johnston]

Author: markj
Date: Thu Mar 21 02:52:22 2019
New Revision: 345359
URL: https://svnweb.freebsd.org/changeset/base/345359

Log:
  Don't attempt to measure TSC skew when running as a VM guest.
  
  It simply doesn't work in general since VCPUs may migrate between
  physical cores.  The approach used to measure skew also doesn't
  make much sense in a VM.
  
  PR:		218452
  MFC after:	2 weeks
  Sponsored by:	The FreeBSD Foundation

Modified:
  head/sys/cddl/dev/dtrace/amd64/dtrace_subr.c
  head/sys/cddl/dev/dtrace/i386/dtrace_subr.c

Modified: head/sys/cddl/dev/dtrace/amd64/dtrace_subr.c
==============================================================================
--- head/sys/cddl/dev/dtrace/amd64/dtrace_subr.c	Thu Mar 21 01:16:37 2019	(r345358)
+++ head/sys/cddl/dev/dtrace/amd64/dtrace_subr.c	Thu Mar 21 02:52:22 2019	(r345359)
@@ -319,6 +319,9 @@ dtrace_gethrtime_init(void *arg)
 	int i;
 #endif
 
+	if (vm_guest)
+		return;
+
 	/* The current CPU is the reference one. */
 	sched_pin();
 	tsc_skew[curcpu] = 0;

Modified: head/sys/cddl/dev/dtrace/i386/dtrace_subr.c
==============================================================================
--- head/sys/cddl/dev/dtrace/i386/dtrace_subr.c	Thu Mar 21 01:16:37 2019	(r345358)
+++ head/sys/cddl/dev/dtrace/i386/dtrace_subr.c	Thu Mar 21 02:52:22 2019	(r345359)
@@ -321,6 +321,9 @@ dtrace_gethrtime_init(void *arg)
 	int i;
 #endif
 
+	if (vm_guest)
+		return;
+
 	/* The current CPU is the reference one. */
 	sched_pin();
 	tsc_skew[curcpu] = 0;