Messages in this thread | | | Subject | Re: [PATCH v8 08/14] nohz_full: allow disabling the 1Hz minimum tick at boot | From | Chris Metcalf <> | Date | Tue, 20 Oct 2015 17:18:13 -0400 |
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On 10/20/2015 05:03 PM, Frederic Weisbecker wrote: > On Tue, Oct 20, 2015 at 04:36:06PM -0400, Chris Metcalf wrote: >> While the current fallback to 1-second tick is still required for >> a number of kernel accounting tasks (e.g. vruntime, load balancing >> data, and load accounting), it's useful to be able to disable it >> for testing purposes. Paul McKenney observed that if we provide >> a mode where the 1Hz fallback timer is removed, this will provide >> an environment where new code that relies on that tick will get >> punished, and we won't forgive such assumptions silently. >> >> This option also allows easy testing of nohz_full and task-isolation >> modes to determine what functionality needs to be implemented, >> and what possibly-spurious timer interrupts are scheduled when >> the basic 1Hz tick has been turned off. >> >> Signed-off-by: Chris Metcalf <cmetcalf@ezchip.com> > There have been proposals to disable/tune the 1 Hz tick via debugfs which > I Nacked because once you give such an opportunity to the users, they > will use that hack and never fix the real underlying issue. > > For the same reasons, I'm sorry but I have to Nack this proposal as well. > > If this is for development or testing purpose, scheduler_max_tick_deferment() is > easily commented out.
Fair enough and certainly your prerogative, so don't hesitate to say "no" to the following argument. :-)
I would tend to differentiate a debugfs proposal from a boot flag proposal: a boot flag is a more hardcore thing to change, and it's not like application developers will come along and explain that you have to boot with different flags to run their app - whereas if they can just sneak in a modification to a debugfs setting that's much easier for the app to tweak.
So perhaps a boot flag is an acceptable compromise between "nothing" and a debugfs tweak? It certainly does make it easier to hack on the task-isolation code, and likely other things where people are trying out fixes to subsystems where they are attempting to remove the reliance on the tick.
-- Chris Metcalf, EZChip Semiconductor http://www.ezchip.com
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