Messages in this thread | | | Date | Tue, 2 Apr 2013 15:09:48 +0200 | Subject | Re: [PATCH 4/4] nohz: New option to force all CPUs in full dynticks range | From | Frederic Weisbecker <> |
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2013/3/30 Ingo Molnar <mingo@kernel.org>: > > * Frederic Weisbecker <fweisbec@gmail.com> wrote: > >> 2013/3/28 Ingo Molnar <mingo@kernel.org>: >> > >> > * Frederic Weisbecker <fweisbec@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.)
All agreed, I'm fixing these issues.
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