Re: [PATCH 1/3] dynticks - implement no idle hz for x86

[Nish Aravamudan <nish.aravamudan@gmail.com>]

On 9/7/05, Srivatsa Vaddagiri <vatsa@in.ibm.com> wrote:
> On Wed, Sep 07, 2005 at 09:42:24AM -0700, Nish Aravamudan wrote:
> > Hrm, got dropped from the Cc... :) Yes, the dynamic-tick generic
> > infrastructure being proposed, with the idle CPU mask and the
> > set_all_cpus_idle() tick_source hook, would allow exactly this in
> > arch-specific code.
> 
> I think Bill is referring to the "resume" interface i.e an
> unset_all_cpus_idle() interface, which is missing (set/unset
> probably are not good prefixes maybe?). I feel we can
> add one.

Yes, can be added.

enter_all_cpus_idle() and exit_all_cpus_idle() would be better?

> > Is there a generic location where the all-idle state is entered?
> 
> Should be from the place where the last cpu is set in the bitmap
> and bitmap is found equal to cpu_online_map.

Yes, this is what I said.

> > Currently, I think we can do it via the generic reprogram() routine
> > checking the mask and then calling set_all_cpus_idle(), if
> > appropriate, after reprogramming the last idle CPU.
> 
> So are you saying that setting of the CPU in the bitmap will be done
> inside reprogram_timer routine? If we consider that reprogram_timer can
> directly point to a routine in a interrupt source file (like apic.c/timer_pit.c)
> I dont think that it is the right place to set bits in the nohz_cpu_mask.
> It can be done by the callee of reprogram_timer itself.

No, I was saying what you were, if a little unclearly, so the caller
does something like:

current_dyn_tick_timer->reprogram();
check_cpu_mask(nohz_cpu_mask);
if (we_are_last_idle)
  enter_all_cpus_idle();

Thanks,
Nish