Re: [PATCH -tip 04/32] sched: Core-wide rq->lock

[Peter Zijlstra]

On Sun, Nov 22, 2020 at 08:11:52PM +1100, Balbir Singh wrote:
> On Tue, Nov 17, 2020 at 06:19:34PM -0500, Joel Fernandes (Google) wrote:
> > From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > 
> > Introduce the basic infrastructure to have a core wide rq->lock.
> >
> 
> Reading through the patch, it seems like all the CPUs have to be
> running with sched core enabled/disabled? Is it possible to have some
> cores with core sched disabled?

Yep, patch even says so:

 + * XXX entirely possible to selectively enable cores, don't bother for now.

> I don't see a strong use case for it,
> but I am wondering if the design will fall apart if that assumption is
> broken?

The use-case I have is not using stop-machine. That is, stopping a whole
core at a time, instead of the whole sodding machine. It's on the todo
list *somewhere*....