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Date: Wed, 13 Apr 2011 23:49:36 +0200
From: Dimitry Andric <dim@FreeBSD.org>
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Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org,
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Subject: Re: svn commit: r220584 - in head/sys: amd64/amd64 i386/i386
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On 2011-04-13 23:41, Dimitry Andric wrote:
...
> But I don't really see why, yet. :)  With r220532, it worked fine.

Ah, I failed to notice the commit that came before, r220583.
Apparently, it can happen (at least in a VM environment) that the
DELAY(1000) in this fragment from cpu_est_clockrate():

                 wrmsr(MSR_MPERF, 0);
                 wrmsr(MSR_APERF, 0);
                 tsc1 = rdtsc();
                 DELAY(1000);
                 mcnt = rdmsr(MSR_MPERF);
                 acnt = rdmsr(MSR_APERF);
                 tsc2 = rdtsc();
                 intr_restore(reg);
                 perf = 1000 * acnt / mcnt;

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?