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xen-devel
RE: [Xen-devel] Time went backwards
> > I have been experimenting with frequency scaling on a 4 core (2
> > sockets) AMD Opteron processors. The versions of Xen I have tested
> > with include xen-testing as well as xen-unstable (cs
> 17042). For both
> > these versions, I am using the linux 2.6.18-8 tree and have passed
> > cpufreq=dom0-kernel to the xen command line.
> >
> > However, I get plenty of "Time went backwards" whenever I attempt to
> > change frequency. Does anyone know how this can be fixed?
> >
> > % grep name /proc/cpuinfo | head -1
> > model name : Dual-Core AMD Opteron(tm) Processor 2216 HE
> >
> > powernow-k8: error - out of sync, fix 0x10 0x10, vid 0xe 0xc
> > powernow-k8: error - out of sync, fix 0x10 0x2, vid 0xc 0x12
>
> Presumably you have cpufreq=dom0-kernel on your Xen command
> line? Apart from
> that noone else has reported 'out of sync' messages from the powernow
> driver. Mark may have some idea what that could be about.
He's got a dual-core system, but the logical grouping of the
cores doesn't match the physical grouping. Something like
cores 0,1 share frequencies, but PowerNow! believes that
cores 0 and 2 do. So when a frequency change on core 0
occurs, the Xen hypervisor gets alerted that cores 0 and 2
have new frequencies. This causes two errors with Xen -
the HV believes core 1 has the old frequency, when it
has the new frequency, and it believes core 2 has the new
frequency, when it really has the old frequency. Time errors
will accumulate rapidly.
Niraj -
Please email me privately. I have some more time to work on
this issue and some new ideas on how to get information about it.
Thanks!
-Mark Langsdorf
Operating System Research Center
AMD
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