svn commit: r220584 - in head/sys: amd64/amd64 i386/i386
Jung-uk Kim
jkim at FreeBSD.org
Wed Apr 13 22:27:47 UTC 2011
On Wednesday 13 April 2011 05:49 pm, Dimitry Andric wrote:
> 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?
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. A simple workaround is setting "machdep.disable_tsc=1"
tuanable from loader but your VM is the real culprit here.
Jung-uk Kim
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