Hey,
On Tue, Jan 12, 2010 at 12:14:29PM +0530, Deepak Sikri wrote:
> The System timer (Clock Source & ClockEvent) for our board is sharing the
> clock with CPU.On changing the CPU frequency using the CPU freq governors,
> we are changing the clock being fed to CPU and timers. This is affecting the
> kernel time keeping as the timer frequecy has been changed. What is the
> mechanism for managing this through the CPU freq/some other Linux Framework
> ?
The CPUfreq framework offers CPU transition notifiers for exactly this
purpose. See e.g. this snippet from arch/x86/kernel/tsc.c:
...
cpufreq_register_notifier(&time_cpufreq_notifier_block,
CPUFREQ_TRANSITION_NOTIFIER);
...
static struct notifier_block time_cpufreq_notifier_block = {
.notifier_call = time_cpufreq_notifier
};
...
static int time_cpufreq_notifier(struct notifier_block *nb, unsigned long val,
void *data)
{
...
if ((val == CPUFREQ_PRECHANGE && freq->old < freq->new) ||
(val == CPUFREQ_POSTCHANGE && freq->old > freq->new) ||
(val == CPUFREQ_RESUMECHANGE)) {
*lpj = cpufreq_scale(loops_per_jiffy_ref, ref_freq, freq->new);
tsc_khz = cpufreq_scale(tsc_khz_ref, ref_freq, freq->new);
...
}
...
}
Hope this helps.
Best,
Dominik
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