Re: [PATCH v8 08/14] nohz_full: allow disabling the 1Hz minimum tick at boot

Frederic Weisbecker
2015-10-20T21:03:38Z

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.