Re: CONFIG_ISOLATION=y (was: [PATCH 0/6] support "dataplane" mode for nohz_full)

Ingo Molnar
2015-05-12T12:34:40Z

* Peter Zijlstra <peterz@infradead.org> wrote:

> On Tue, May 12, 2015 at 11:10:32AM +0200, Ingo Molnar wrote:
> >
> > So I'd vote for Frederic's CONFIG_ISOLATION=y, mostly because this
> > is a high level kernel feature, so it won't conflict with
> > isolation concepts in lower level subsystems such as IOMMU
> > isolation - and other higher level features like scheduler
> > isolation are basically another partial implementation we want to
> > merge with all this...
>
> But why do we need a CONFIG flag for something that has no content?
>
> That is, I do not see anything much; except the 'I want to stay in
> userspace and kill me otherwise' flag, and I'm not sure that
> warrants a CONFIG flag like this.
>
> Other than that, its all a combination of NOHZ_FULL and
> cpusets/isolcpus and whatnot.

Yes, that's what I meant: CONFIG_ISOLATION would trigger what is
NO_HZ_FULL today - we could possibly even remove CONFIG_NO_HZ_FULL as
an individual Kconfig option?

CONFIG_ISOLATION=y would express the guarantee from the kernel that
it's possible for user-space to configure itself to run undisturbed -
instead of the current inconsistent set of options and facilities.

A bit like CONFIG_PREEMPT_RT is more than just preemptable spinlocks,
it also tries to offer various facilities and tune the defaults to
turn the kernel hard-rt.

Does that make sense to you?

Thanks,

Ingo