about system time incorrect after changing cpu frequency

[vichy]

hi Jisheng:

2015-09-01 14:39 GMT+08:00 Jisheng Zhang <jszhang at marvell.com>:
> On Tue, 1 Sep 2015 11:32:36 +0530
> Viresh Kumar <viresh.kumar at linaro.org> wrote:
>
>> On 01-09-15, 13:36, vichy wrote:
>> > >> I try to call below 2 functions to change the frequency of clocksource
>> > >> and clockevent, but the above b) sleep time is still incorrect when
>> > >> cpu runs in 500Mhz.
>> > >>     clockevents_update_freq(this_cpu_ptr(gt_evt), gt_clk_rate);
>> > >>     __clocksource_updatefreq_hz(&gt_clocksource, gt_clk_rate);
>>
>> How and when were you calling them? What kernel version is it ?
>>
>> > Clock Event Device: arm_global_timer
>>
>> This driver doesn't have support to update clkevt device's freq. You
>> may need to modify that based on how arch/arm/kernel/smp_twd.c is
>> updated. look for: clockevents_update_freq().
>>
>
> This can only help the clockevent. Even with this cpufreq notifier
> update, the globaltimer clocksource still can't hold correct/accurate time.
Why even global timer add clockevents_update_freq, it stilll CANNOT
hold currect/accurate time?
When I trace the kernel, clockevents_program_event will calculate the
cycles with mult/shift then put in comparator.
if we put the write mult/shift, the global  timer should hold
correct/accurate time under different phepherial clock, right?

Appreciate all your kind help,