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From: Christopher Lameter <cl@linux.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: cmetcalf@mellanox.com, linux-kernel@vger.kernel.org,
	tglx@linutronix.de, torvalds@linux-foundation.org, hpa@zytor.com,
	riel@redhat.com, mingo@kernel.org, efault@gmx.de,
	frederic@kernel.org, kernellwp@gmail.com,
	paulmck@linux.vnet.ibm.com, lcapitulino@redhat.com,
	linux-tip-commits@vger.kernel.org
Subject: Re: [tip:sched/core] sched/isolation: Document the isolcpus= flags
Date: Mon, 30 Oct 2017 11:30:59 -0500 (CDT)	[thread overview]
Message-ID: <alpine.DEB.2.20.1710301125060.1182@nuc-kabylake> (raw)
In-Reply-To: <20171030161101.wprohopz5eg7snb4@hirez.programming.kicks-ass.net>

On Mon, 30 Oct 2017, Peter Zijlstra wrote:

> > 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.

Well yes a cpuset of one processor I guess.

> > 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.
>
> > cgroup has to do something with containers
>
> Sod containers. That's just modern group think. cpusets existed long
> before all that wankery and it should very well retain the original use
> cases.

Historically cpusets were not used for cpu isolation. They were used to
restrict applications threads to sets of cpus for performance reasons. And
we are here dealing with individual processors.

> That said, I know there's problems with cpusets, and those should be
> fixed. But that doesn't mean isolcpus is anything other than a vile
> hack.

Controlling the way an individual processor works would be best done with
some kind of configuration in sysfs. I.e. /sys/cpu/<xx>/no_sched or so.

In lieu of that I think isolcpus is definitely better than a cpuset and it
is the only way that traditionally processor handling of the OS has been
restricted.

  reply	other threads:[~2017-10-30 16:31 UTC|newest]

Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-10-27  2:42 [GIT PULL] Housekeeping subsystem v6 Frederic Weisbecker
2017-10-27  2:42 ` [PATCH 01/12] housekeeping: Move housekeeping related code to its own file Frederic Weisbecker
2017-10-27 12:01   ` [tip:sched/core] sched/isolation: " tip-bot for Frederic Weisbecker
2017-10-27  2:42 ` [PATCH 02/12] watchdog: Use housekeeping_cpumask() instead of ad-hoc version Frederic Weisbecker
2017-10-27 12:02   ` [tip:sched/core] sched/isolation, " tip-bot for Frederic Weisbecker
2017-10-27  2:42 ` [PATCH 03/12] housekeeping: Provide a dynamic off-case to housekeeping_any_cpu() Frederic Weisbecker
2017-10-27 12:02   ` [tip:sched/core] sched/isolation: " tip-bot for Frederic Weisbecker
2017-10-27  2:42 ` [PATCH 04/12] housekeeping: Make housekeeping cpumask private Frederic Weisbecker
2017-10-27 12:03   ` [tip:sched/core] sched/isolation: Make the " tip-bot for Frederic Weisbecker
2017-10-27  2:42 ` [PATCH 05/12] housekeeping: Use its own static key Frederic Weisbecker
2017-10-27 12:03   ` [tip:sched/core] sched/isolation: " tip-bot for Frederic Weisbecker
2017-10-27  2:42 ` [PATCH 06/12] housekeeping: Rename is_housekeeping_cpu to housekeeping_cpu Frederic Weisbecker
2017-10-27 12:03   ` [tip:sched/core] sched/isolation: Rename is_housekeeping_cpu() to housekeeping_cpu() tip-bot for Frederic Weisbecker
2017-10-27  2:42 ` [PATCH 07/12] housekeeping: Move it under its own config, independent from NO_HZ Frederic Weisbecker
2017-10-27 12:04   ` [tip:sched/core] sched/isolation: Split out new CONFIG_CPU_ISOLATION=y config from CONFIG_NO_HZ_FULL tip-bot for Frederic Weisbecker
2017-10-27  2:42 ` [PATCH 08/12] housekeeping: Introduce housekeeping flags Frederic Weisbecker
2017-10-27 12:04   ` [tip:sched/core] sched/isolation: " tip-bot for Frederic Weisbecker
2017-10-27  2:42 ` [PATCH 09/12] housekeeping: Handle the nohz_full= parameter Frederic Weisbecker
2017-10-27 12:05   ` [tip:sched/core] sched/isolation: " tip-bot for Frederic Weisbecker
2017-10-27  2:42 ` [PATCH 10/12] housekeeping: Move isolcpus to housekeeping Frederic Weisbecker
2017-10-27 12:05   ` [tip:sched/core] sched/isolation: Move isolcpus= handling to the housekeeping code tip-bot for Frederic Weisbecker
2017-10-27  2:42 ` [PATCH 11/12] housekeeping: Add basic isolcpus flags Frederic Weisbecker
2017-10-27 12:05   ` [tip:sched/core] sched/isolation: " tip-bot for Frederic Weisbecker
2017-10-27  2:42 ` [PATCH 12/12] housekeeping: Document " Frederic Weisbecker
2017-10-27 12:06   ` [tip:sched/core] sched/isolation: Document the isolcpus= flags tip-bot for Frederic Weisbecker
2017-10-27 13:58     ` Peter Zijlstra
2017-10-27 14:36       ` Frederic Weisbecker
2017-10-27 17:06         ` Ingo Molnar
2017-10-27 17:33           ` Frederic Weisbecker
2017-10-27 18:21             ` Ingo Molnar
2017-10-27 18:39               ` Frederic Weisbecker
2017-10-27 19:04                 ` Ingo Molnar
2017-10-27 14:38       ` Mike Galbraith
2017-10-30 15:48       ` Christopher Lameter
2017-10-30 16:11         ` Peter Zijlstra
2017-10-30 16:30           ` Christopher Lameter [this message]
2017-10-30 16:58             ` Peter Zijlstra
2017-10-30 16:56           ` Mike Galbraith

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