RE: [PATCH] Option to synchronize P-states for AMD family 0xf

Langsdorf, Mark
2009-09-30T14:31:21Z

> > AMD Family 0xf processors (Athlon 64s and Opterons) do not
> > have P-State or C-State invariant TSCs. Instead, the TSC
> > increments at the current processor frequency, which makes
> > it unstable and unreliable if cpufreq is enabled.
> >
> > This patch introduces a new command parameter for the
> > PowerNow! driver called "tscsync". When tscsync is
> > set to 1, the driver forces all processors in the system
> > to change frequency as the same time to the same frequency.
> > This unified change means that all the TSCs in the system
> > increment at the same rate.
>
> Cool feature. Does Linux consider the TSC as stable on these machines
> even after a longer uptime (say after a week)?

Ask me in a week. Linux time-keeping code has evolved
quite a bit since I last looked at this code.

-Mark Langsdorf
Operating System Research Center
AMD