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

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Date:   Mon, 30 Oct 2017 17:56:25 +0100
From:   Mike Galbraith <efault@....de>
To:     Peter Zijlstra <peterz@...radead.org>,
        Christopher Lameter <cl@...ux.com>
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, 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 Mon, 2017-10-30 at 17:11 +0100, Peter Zijlstra wrote:
> On Mon, Oct 30, 2017 at 10:48:04AM -0500, Christopher Lameter wrote:
> > 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.
> 
> That is what you want, and cpusets should allow for that just fine.
> 
> > A cgroup suggests that threads would be scheduled over multiple cores
> > which is *not* what you want.
> 
> No, that suggestion is false. cpusets should allow you to isolate
> individual CPUs just fine.

It does.  I do RT jitter testing with it regularly.  If it didn't work,
my 8 socket box would let me know instantly, by completely sucking :)

	-Mike