linux-kernel - Re: [PATCH v4] cpuset: Enable cpuset controller in default hierarchy

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Date:   Sat, 10 Mar 2018 04:47:28 +0100
From:   Mike Galbraith <efault@....de>
To:     Waiman Long <longman@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Tejun Heo <tj@...nel.org>, Li Zefan <lizefan@...wei.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Ingo Molnar <mingo@...hat.com>, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        kernel-team@...com, pjt@...gle.com, luto@...capital.net,
        torvalds@...ux-foundation.org, Roman Gushchin <guro@...com>
Subject: Re: [PATCH v4] cpuset: Enable cpuset controller in default hierarchy

On Fri, 2018-03-09 at 18:06 -0500, Waiman Long wrote:
> On 03/09/2018 05:17 PM, Peter Zijlstra wrote:
> > On Fri, Mar 09, 2018 at 03:43:34PM -0500, Waiman Long wrote:
> >> The isolcpus= parameter just reduce the cpus available to the rests of
> >> the system. The cpuset controller does look at that value and make
> >> adjustment accordingly, but it has no dependence on exclusive cpu/mem
> >> features of cpuset.
> > The isolcpus= boot param is donkey shit and needs to die. cpuset _used_
> > to be able to fully replace it, but with the advent of cgroup 'feature'
> > this got lost.
> >
> > And instead of fixing it, you're making it _far_ worse. You completely
> > removed all the bits that allow repartitioning the scheduler domains.
> >
> > Mike is completely right, full NAK on any such approach.
> 
> So you are talking about sched_relax_domain_level and
> sched_load_balance. I have not removed any bits. I just haven't exposed
> them yet. It does seem like these 2 control knobs are useful from the
> scheduling perspective. Do we also need cpu_exclusive or just the two
> sched control knobs are enough?

Some form of cpu_exclusive (preferably exactly that, but something else
could replace it) is needed to define sets that must not overlap any
other set at creation time or any time thereafter.  A set with property
'exclusive' is the enabler for fundamentally exclusive (but dynamic!)
set properties such as 'isolated' (etc etc).

	-Mike