hi Viresh:
2015-09-01 11:57 GMT+08:00 Viresh Kumar <viresh.kumar@xxxxxxxxxx>:
> On Mon, Aug 31, 2015 at 7:33 PM, vichy <vichy.kuo@xxxxxxxxx> wrote:
>> hi all:
>> My platform is like below:
>> 1. single core Cortex A9
>> 2. use global timer for system timer
>>
>> after I porting cpu frequency driver based on snow ball, the cpu
>> frequency did change as I expected.
>> But the system time is incorrect( since pherial clk is got from cpu frequency)
>>
>> for example:
>> a) cpu 1G (pherial clk = 250M) --> sleep 1 sec (OK)
>> b) cpu 500M (pherial clk = 125M) --> sleep 1 sec (will be measured as 2 sec)
>>
>> 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(>_clocksource, gt_clk_rate);
>>
>> in Arm cortex A9 single core system with Global timer as system timer,
>> is there any kernel api to change system timer period when cpu/pherial
>> frequency change?
>>
>> appreciate your kind help in advance,
>
> The list cpufreq@xxxxxxxxxxxxxxx is the wrong list for posting cpufreq queries
> as we have moved to Linux PM list <linux-pm@xxxxxxxxxxxxxxx> list now.
>
> Try unsetting CPUFREQ_CONST_LOOPS flag in your driver, if you have it
> set.
I DIDN'T set the CPUFREQ_CONST_LOOPS when I register my cpufreq driver
I pasted my cpufreq driver declariation as below:
static struct cpufreq_driver plat_cpufreq_driver = {
.flags = CPUFREQ_STICKY,
.verify = plat_cpufreq_verify_speed,
.target = plat_cpufreq_target,
.get = plat_cpufreq_getspeed,
.init = plat_cpufreq_init,
.name = "plat-cpufreq",
.attr = plat_cpufreq_attr,
};
I have traced the kernel code
if I guess correctly, the sleep accurate is based on jiffies and
tick_handle_periodic will periodically update the next event interval
void tick_handle_periodic
-->
for (;;) {
if (!clockevents_program_event(dev, next, false))
return;
/*
* Have to be careful here. If we're in oneshot mode,
* before we call tick_periodic() in a loop, we need
* to be sure we're using a real hardware clocksource.
* Otherwise we could get trapped in an infinite
* loop, as the tick_periodic() increments jiffies,
* when then will increment time, posibly causing
* the loop to trigger again and again.
*/
if (timekeeping_valid_for_hres())
tick_periodic(cpu);
next = ktime_add(next, tick_period);
}
and in clockevents_program_event, we will use mult, shift to calculate
the cycles need for global timer triggering next interrupt event.
clc = ((unsigned long long) delta * dev->mult) >> dev->shift;
rc = dev->set_next_event((unsigned long) clc, dev);
belwo is my tick device information in /proc/timer_list
and multi did change to 1/2 when I change cpu freq from 1G to 500Mhz.
when cpu run 1GHz
except multi and shift, is there any place I need to take care for
system timer accurate?
appreciate your kind help,
Tick Device: mode: 1
Per CPU device: 0
Clock Event Device: arm_global_timer
max_delta_ns: 17043521021
min_delta_ns: 1000
mult: 541165879
shift: 31
mode: 3
next_event: 2176344000000 nsecs
set_next_event: gt_clockevent_set_next_event
set_mode: gt_clockevent_set_mode
event_handler: hrtimer_interrupt
retries: 0
when cpu run in 500Mhz
Tick Device: mode: 1
Per CPU device: 0
Clock Event Device: arm_global_timer
max_delta_ns: 34087041979
min_delta_ns: 1000
mult: 270582940
shift: 31
mode: 3
next_event: 2230100000000 nsecs
set_next_event: gt_clockevent_set_next_event
set_mode: gt_clockevent_set_mode
event_handler: hrtimer_interrupt
retries: 0
--
To unsubscribe from this list: send the line "unsubscribe cpufreq" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
