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

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Message-ID: <alpine.DEB.2.20.1708281032340.13971@nuc-kabylake>
Date:   Mon, 28 Aug 2017 10:38:01 -0500 (CDT)
From:   Christopher Lameter <cl@...ux.com>
To:     Peter Zijlstra <peterz@...radead.org>
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 Mon, 28 Aug 2017, Peter Zijlstra wrote:

> > 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.

Well the next step was to create a cgroup with those processors and
suddenly load balancing worked again.

This is all pretty confusing stuff. I would rather get rid of isolcpus and
rely on the process affinities set to a single processor, and the removal
of the this processor from all other processes as a sufficient.

I think this already does the right thing. What is mentioned in the isolcpus
documentation is a worry about "suboptimal scheduler performance".

Could we address that issue (if it is still there) and then get rid of
isolcpus?