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

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Message-ID: <20170828101022.t26ikxslcf2c5bcl@hirez.programming.kicks-ass.net>
Date:   Mon, 28 Aug 2017 12:10:22 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Christopher Lameter <cl@...ux.com>
Cc:     Frederic Weisbecker <fweisbec@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Chris Metcalf <cmetcalf@...lanox.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Luiz Capitulino <lcapitulino@...hat.com>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        Ingo Molnar <mingo@...nel.org>, Mike Galbraith <efault@....de>,
        Rik van Riel <riel@...hat.com>,
        Wanpeng Li <kernellwp@...il.com>
Subject: Re: [RFC PATCH 12/12] housekeeping: Reimplement isolcpus on
 housekeeping

On Wed, Aug 23, 2017 at 09:55:51AM -0500, Christopher Lameter wrote:
> On Wed, 23 Aug 2017, Frederic Weisbecker wrote:
> 
> > 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.
> 
> I think that change is good maybe even a bugfix. I had some people be very
> surprised when they set affinities to multiple cpus and the processeds
> kept sticking to one cpu because of isolcpus.

Those people cannot read. And no its not a bug fix. Its documented and
intended behaviour.