Enabling tickless kernel feature in ARM

Mulyadi Santosa mulyadi.santosa at gmail.com
Tue Apr 26 12:35:13 EDT 2011

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


Mulyadi Santosa
Freelance Linux trainer and consultant

blog: the-hydra.blogspot.com
training: mulyaditraining.blogspot.com

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