Date: Thu, 14 Apr 2011 12:49:41 +0200 From: Dimitry Andric <dim@FreeBSD.org> To: Jung-uk Kim <jkim@FreeBSD.org> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org Subject: Re: svn commit: r220584 - in head/sys: amd64/amd64 i386/i386 Message-ID: <4DA6D145.8070804@FreeBSD.org> In-Reply-To: <201104131827.39373.jkim@FreeBSD.org> References: <201104122349.p3CNn7kK039179@svn.freebsd.org> <4DA6189A.5040200@FreeBSD.org> <4DA61A70.8040609@FreeBSD.org> <201104131827.39373.jkim@FreeBSD.org>
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This is a multi-part message in MIME format. --------------090705030302090306020404 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit On 2011-04-14 00:27, Jung-uk Kim wrote: ... >> will still read 0 from MSR_MPERF, leading to a division by zero. >> Maybe just fallback to the second method in the 'else' branch then? > > That means your VM has broken CPUID support. To get there, it has to > meet two conditions, i.e., TSC is invariant and it has APERF/MPERF > MSRs. Well, VM hosts like VMware and VirtualBox usually just return the 'native' CPUID values to guests, but can't really support stuff like those MSRs, for all kinds of reasons. I was just looking at this from a viewpoint of "it worked for years, and now it broke". :) In any case, I don't see why a bit of defensive programming would be bad here, so I propose the following patch to revert to the 'old' way of estimating the rate, in case reading the MPERF MSR returns zero. --------------090705030302090306020404 Content-Type: text/plain; name="est-zero-mcnt-workaround-1.diff" Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename="est-zero-mcnt-workaround-1.diff" Index: sys/i386/i386/machdep.c =================================================================== --- sys/i386/i386/machdep.c (revision 220620) +++ sys/i386/i386/machdep.c (working copy) @@ -1172,7 +1172,7 @@ cpu_est_clockrate(int cpu_id, uint64_t *rate) acnt = rdmsr(MSR_APERF); tsc2 = rdtsc(); intr_restore(reg); - perf = 1000 * acnt / mcnt; + perf = (mcnt != 0) ? 1000 * acnt / mcnt : 1000; *rate = (tsc2 - tsc1) * perf; } else { tsc1 = rdtsc(); Index: sys/amd64/amd64/machdep.c =================================================================== --- sys/amd64/amd64/machdep.c (revision 220620) +++ sys/amd64/amd64/machdep.c (working copy) @@ -579,7 +579,7 @@ cpu_est_clockrate(int cpu_id, uint64_t *rate) acnt = rdmsr(MSR_APERF); tsc2 = rdtsc(); intr_restore(reg); - perf = 1000 * acnt / mcnt; + perf = (mcnt != 0) ? 1000 * acnt / mcnt : 1000; *rate = (tsc2 - tsc1) * perf; } else { tsc1 = rdtsc(); --------------090705030302090306020404--
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