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;
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