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

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Message-ID: <20171027135831.GZ3165@worktop.lehotels.local>
Date:   Fri, 27 Oct 2017 15:58:31 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     cmetcalf@...lanox.com, linux-kernel@...r.kernel.org,
        tglx@...utronix.de, torvalds@...ux-foundation.org, hpa@...or.com,
        riel@...hat.com, cl@...ux.com, mingo@...nel.org, efault@....de,
        frederic@...nel.org, kernellwp@...il.com,
        paulmck@...ux.vnet.ibm.com, lcapitulino@...hat.com
Cc:     linux-tip-commits@...r.kernel.org
Subject: Re: [tip:sched/core] sched/isolation: Document the isolcpus= flags

On Fri, Oct 27, 2017 at 05:06:25AM -0700, tip-bot for Frederic Weisbecker wrote:
> +	isolcpus=	[KNL,SMP] Isolate a given set of CPUs from disturbance.
> +			Format: [flag-list,]<cpu-list>
> +
> +			Specify one or more CPUs to isolate from disturbances
> +			specified in the flag list (default: domain):
> +
> +			nohz
> +			  Disable the tick when a single task runs.
> +			domain
> +			  Isolate from the general SMP balancing and scheduling
> +			  algorithms. This option is the preferred way to isolate
> +			  CPUs from tasks. 

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.

> The alternative -- manually setting the
> +			  CPU mask of all tasks in the system, can cause problems
> +			  and suboptimal load balancer performance. You can move a
> +			  process onto or off an "isolated" CPU via the CPU
> +			  affinity syscalls or cpuset. <cpu number> begins at 0
> +			  and the maximum value is "number of CPUs in system - 1".
> +
> +			The format of <cpu-list> is described above.
> +