linux-kernel - Re: [tip:sched/core] sched/isolation: Document the isolcpus= flags

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Message-ID: <alpine.DEB.2.20.1710301045160.970@nuc-kabylake>
Date:   Mon, 30 Oct 2017 10:48:04 -0500 (CDT)
From:   Christopher Lameter <cl@...ux.com>
To:     Peter Zijlstra <peterz@...radead.org>
cc:     cmetcalf@...lanox.com, linux-kernel@...r.kernel.org,
        tglx@...utronix.de, torvalds@...ux-foundation.org, hpa@...or.com,
        riel@...hat.com, mingo@...nel.org, efault@....de,
        frederic@...nel.org, kernellwp@...il.com,
        paulmck@...ux.vnet.ibm.com, lcapitulino@...hat.com,
        linux-tip-commits@...r.kernel.org
Subject: Re: [tip:sched/core] sched/isolation: Document the isolcpus= flags

On Fri, 27 Oct 2017, Peter Zijlstra wrote:

> I _strongly_ object to this statement, isolcpus is _not_ the preferred
> way, cpusets are.
>
> And yes, while cpusets suffers some problems, we _should_ really fix
> those and not promote this piece of shit isolcpus crap.

Well low level control at the processor level is important and this allows
controlling activities on a processor that is supposed to be dedicated to
certain activities without OS interaction.

isolcpus is the *right* approach here because you are micromanaging the OS
and are putting dedicated pieces of software on each core.

A cgroup suggests that threads would be scheduled over multiple cores
which is *not* what you want. cgroup has to do something with containers
etc which is inherently more noisy and needed if you want to do different
things with your processing resources.