Date: Wed, 20 Mar 2019 20:20:18 -0700 (PDT) From: "Rodney W. Grimes" <freebsd@gndrsh.dnsmgr.net> To: Mark Johnston <markj@freebsd.org> Cc: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r345359 - in head/sys/cddl/dev/dtrace: amd64 i386 Message-ID: <201903210320.x2L3KIjc058579@gndrsh.dnsmgr.net> In-Reply-To: <201903210252.x2L2qMSP022374@repo.freebsd.org>
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> 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. "May" is the important aspect here, and to my knowledge both bhyve and Vmware provide a way to pin cpus there should be a way for us to turn this back on if it is desired. Sticking it under the big knob vm_guest is probably not the most flexiable solution. Could we please have someway to force this back on? > > 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; > > -- Rod Grimes rgrimes@freebsd.org
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