* Frederic Weisbecker <fweis...@gmail.com> wrote:
> 2013/3/28 Ingo Molnar <mi...@kernel.org>:
> >
> > * Frederic Weisbecker <fweis...@gmail.com> wrote:
> >
> >> +config NO_HZ_EXTENDED_ALL
> >> + bool "Full dynticks system on all CPUs"
> >> + depends on NO_HZ_EXTENDED
> >> + help
> >> + Force all CPUs to be full dynticks. The range specified in the
> >> + nohz_extended boot option will then be ignored.
> >> +
> >> + Note the boot CPU will still be kept outside the range to handle
> >> + the timekeeping duty.
> >
> > In most cases this will be the first time users doing 'make oldconfig'
> > will hear about this feature, so I'd not mention noh_extended in such a
> > primary way at all.
> >
> > Instead I'd suggest to explain, in a few simple sentences, what 'full
> > dynticks' _is_. Then maybe mention this near the end of the next:
> >
> > ( Alternatively this feature can also be enabled via the
> > nohz_extended=<cpulist> boot option. If this kernel config option is
> > enabled then the nohz_extended boot parameter is ignored. )
>
> Ok. Hmm, concerning what full dynticks is, those who run make oldconfig
> should have passed through CONFIG_NO_HZ_EXTENDED help first so they
> should know what this is all about, right? I can improve its help text
> if you think something need more details. Or you think I should add some
> more reminder in the new config? Also nohz_extended is not mentioned
> there so I indeed need to fix that. And then do a reminder in the new
> config. I'll reuse a bit your above sentence.
Kconfig option + boot parameter, or kconfig option + kconfig option, just
to get a feature to activate, is usability madness.
I think we need _one_ config knob to configure, which, if selected,
activates all of this feature. Preferably this would be similar to the
preempt options, like CONFIG_PREEMPT is the most advanced preemption
model:
( ) No Forced Preemption (Server)
(X) Voluntary Kernel Preemption (Desktop)
( ) Preemptible Kernel (Low-Latency Desktop)
NO_HZ_EXTENDED or NO_HZ_FULL could be a third variant to:
( ) Periodic Timer Ticks
(X) Tickless Idle (Dynamic Ticks)
( ) Full Tickless (Extended Dynamic Ticks)
or so - instead of this somewhat confusing hierarchy of config and boot
options. Good help text would explain the differences between then.
Internally, the 'Tickless Idle' option would cause NO_HZ to be set, while
'Full Tickless' would also set NO_HZ, but would also set NO_HZ_EXTENDED.
Furthermore, right now it's hard to enable NO_HZ_EXTENDED, because it
depends on so many other options. The option is just hidden unless the
user knows about it and enables 5 other kernel options. Instead the tick
mode selected should enable (select) any required features - it should
drive things, not the other way around.
(After all that is done, the boot option is something that augments this
existing, kconfig driven mechanism.)
Thanks,
Ingo
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