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

Frederic Weisbecker
2015-10-21T15:35:09Z

On Wed, Oct 21, 2015 at 09:28:04AM -0500, Christoph Lameter wrote:
> On Tue, 20 Oct 2015, Frederic Weisbecker wrote:
>
> > 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.
>
> Well this is a pretty bad argument. By that reasoning no one should be
> allowed to use root. After all stupid users will become root and kill
> processes that are hung. And the underlying issue that causes those hangs
> in processes will never be fixed because they will keep on killing
> processes.

I disagree. There is an signifiant frontier between:

_ hack it up and you're responsible of the consequences, yourself

and

_ provide a buggy hack to the user and support this officially upstream

Especially as all I've seen in two years, wrt. solving the 1 Hz issue, is patches like this.
Almost nobody really tried to dig into the real issues that are well known and identified
after all now, and not that hard to fix: it's many standalone issues to make the scheduler
resilient with full-total-hard-dynticks.

The only effort toward that I've seen lately is: https://lkml.org/lkml/2015/10/14/192
and still I think the author came to that nohz issue by accident.

Many users are too easily happy with hacks like this and that one is a too much a good
opportunity for them.