Enabling tickless kernel feature in ARM

[Vikram Narayanan]

Dear Haojian,

On Tue, Apr 26, 2011 at 10:04 PM, Haojian Zhuang
<haojian.zhuang at gmail.com> wrote:
>
> On Tue, Apr 26, 2011 at 9:55 PM, 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.
> > There was one struct by the name dyn_tick_timer, which is located
> > under linux/include/asm-arm/mach/time.h file. (which is removed from v
> > 2.6.27)
> > Now my question is that, are all the dyn_tick_timer functionalities
> > are moved to a generic interface somewhere?
> CONFIG_NO_HZ is used instead.

I am aware of the CONFIG_NO_HZ option. I am asking about the
implementation of it. To put in a more clear way.
There was a structure in the kernel source
linux/include/asm-arm/mach/time.h before 2.6.27

struct dyn_tick_timer {
          spinlock_t      lock;
          unsigned int    state;                  /* Current state */
          int             (*enable)(void);        /* Enables dynamic tick */
          int             (*disable)(void);       /* Disables dynamic tick */
          void            (*reprogram)(unsigned long); /* Reprograms
the timer */
          int             (*handler)(int, void *);
  };

To enable dynamic tick timer, one should implement functions for
enable, disable and reprogram. But this structure is no more used in
the new kernel source. In 2007 linux symposium, 3 authors talked about
implementing the tickless feature using HPET timers. Now my question
where does the implementation lies in the ARM architecture.

Vikram
>
> > Are the clock source and clockevent device timers enough to take care
> > of the tickless feature?
> There's no relationship between NOHZ and clocksource/clockevent.
> >
> > -
> > Vikram
> >
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> >