Re: [RFC PATCH 12/12] housekeeping: Reimplement isolcpus on housekeeping

[Frederic Weisbecker]

On Mon, Aug 28, 2017 at 12:09:57PM +0200, Peter Zijlstra wrote:
> On Wed, Aug 23, 2017 at 03:51:11AM +0200, Frederic Weisbecker wrote:
> > We want to centralize the isolation features on the housekeeping
> > subsystem and scheduler isolation is a significant part of it.
> > 
> > While at it, this is a proposition for a reimplementation of isolcpus=
> > that doesn't involve  scheduler domain isolation. Therefore this
> > brings a behaviour change: all user tasks inherit init/1 affinity which
> > avoid the isolcpus= range. But if a task later overrides its affinity
> > which turns out to intersect an isolated CPU, load balancing may occur
> > on it.
> > 
> > OTOH such a reimplementation that doesn't shortcut scheduler internals
> > makes a better candidate for an interface extension to cpuset.
> 
> Not sure we can do this. It'll break users that rely on the no
> scheduling thing, that's a well documented part of isolcpus.

That was my worry :-s  That NULL domain was probably a design mistake and
I fear we now have to maintain it.