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Date:   Tue, 24 Nov 2020 09:16:17 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Balbir Singh <bsingharora@gmail.com>
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Subject: Re: [PATCH -tip 04/32] sched: Core-wide rq->lock
Message-ID: <20201124081617.GT3021@hirez.programming.kicks-ass.net>
References: <20201117232003.3580179-1-joel@joelfernandes.org>
 <20201117232003.3580179-5-joel@joelfernandes.org>
 <20201122091152.GB110669@balbir-desktop>
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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@infradead.org>
> > 
> > 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*....