Re: [GIT PULL] nohz: Adaptively stop the tick, finally

Frederic Weisbecker
2013-04-24T14:50:44Z

On Wed, Apr 24, 2013 at 09:38:52AM +0200, Ingo Molnar wrote:
>
> * Ingo Molnar <mingo@kernel.org> wrote:
>
> > One detail: 'make oldconfig' gave me:
> >
> > Timer tick handling
> > 1. Periodic timer ticks (constant rate, no dynticks) (HZ_PERIODIC) (NEW)
> > > 2. Idle dynticks system (tickless idle) (NO_HZ_IDLE) (NEW)
> >
> > I.e. CONFIG_NO_HZ_IDLE is picked by default. The default should really be
> > CONFIG_HZ_PERIODIC - so that people can easily enable full dynticks but
> > are not defaulted into it unknowingly.
>
> Oh, I got confused by the artificial hiding of NO_HZ_FULL again. Why is it
> still hidden? I have a fairly generic config, yet it was not offered. I
> bet most people won't ever see it!
>
> Sigh, it's due to the dependency mess that I pointed out twice already:
>
> depends on TREE_RCU || TREE_PREEMPT_RCU

Ok I just removed this one. This was the same as "depends on SMP" which we already
have.

> depends on VIRT_CPU_ACCOUNTING_GEN
>
> It should _really_ select both the RCU and the CPU time accounting model
> automatically!

Yeah I know. I have yet to fix that in Kconfig (it's a Kconfig limitation).
It's high on my TODO list.

>
> The selection of the dynticks mode certainly overrides RCU selection, and
> it should for sure override some arcane, low level detail like the CPU
> accounting model ...

Agreed, that was not intended to stay as is.

Thanks.