tickless/dynticks + cpufreq = tsc unstable

tickless/dynticks + cpufreq = tsc unstable

[Michael Tokarev]

Is it normal that once I enable cpufreq on
a tickless system, it spews a warning:

Clocksource tsc unstable (delta = -288201154 ns)

?

It's an old problem, and I was thinking about
differences between x86-64 (it worked there) and
i386 kernels.  But with 2.6.24, x86-64 can run
tickless as well, and once I enable this mode,
and load dynamic cpufreq governor, the above message
gets printed too.

The system is amd x2-64, all kernels since tickless
has been introduced.

I'm not sure if it's really something to worry about --
probably not, as this system has hpet.  But on another
system, Intel-based, where there was no hpet and jiffies
clocksourse gets selected instead, there were some...
issues still (I don't remember offhand which ones, will
check the next week with new kernel).

Thanks!

/mjt

Re: tickless/dynticks + cpufreq = tsc unstable

[Lee Revell]

On Jan 25, 2008 6:02 PM, Michael Tokarev <mjt@tls.msk.ru> wrote:
> Is it normal that once I enable cpufreq on
> a tickless system, it spews a warning:
>
> Clocksource tsc unstable (delta = -288201154 ns)
>
> ?

Yes, it's normal.  Dual core AMD64 machines really do have unstable TSC.

Lee