Enabling tickless kernel feature in ARM

[Vikram Narayanan]

Dear,

On Tue, Apr 26, 2011 at 10:05 PM, Mulyadi Santosa
<mulyadi.santosa at gmail.com> wrote:
> Dear Vikram...
>
> On Tue, Apr 26, 2011 at 20:55, Vikram Narayanan <vikram186 at gmail.com> wrote:
>> Hi,
>>
>> I want to enable the dynamic tick aka tickless kernel feature for the
>> BSP which I am developing. What are all the architecture dependent
>> changes that needs to be done for implementing it.
>
> To the best I know:
>
> essentially, to achieve tickless ( also know as "no hz"), you need to
> reprogram your timer chip, so it just "shoot" whenever needed, not
> periodically. And sometimes, you need to round them up, i.e there are
> timers which expires in the next 10 ms, 11 ms and 15 ms...so
> effectively, better to make them expire at 15 ms if possible.
>
> so, you need a way to detect the timer expiration (possibly by walking
> through active timer list) and decide when the timer chip needs to
> shoot interrupt. The rest of the change...of course...still needed
> further thinking....
>
> NB: AFAIK In x86, HPET is a prerequisite to achieve tickless... maybe
> because reprogramming HPET is somewhat way faster than regular PIT
I have read about the dynamic tick feature in lwn.net. When I see the
source, it seems to have implemented only with the HPET timers. and
also, these dynamic ticks are achieved with hrtimers nowadays.
http://lxr.linux.no/#linux+v2.6.38/Documentation/timers/highres.txt#L204
Also I believe most of the implementation is moved to the arch
independent part with the help of clocksource and clockevents.
Do I need to enable hrtimers for enabling the dynamic tick feature.?

-
Thanks
Vikram
>
> --
> regards,
>
> Mulyadi Santosa
> Freelance Linux trainer and consultant
>
> blog: the-hydra.blogspot.com
> training: mulyaditraining.blogspot.com
>