linux-kernel - Re: [PATCH 1/3] cgroup: define controller file conventions

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Message-ID: <20150804084855.GK25159@twins.programming.kicks-ass.net>
Date:	Tue, 4 Aug 2015 10:48:55 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	mingo@...hat.com, hannes@...xchg.org, lizefan@...wei.com,
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel-team@...com
Subject: Re: [PATCH 1/3] cgroup: define controller file conventions

On Mon, Aug 03, 2015 at 06:41:27PM -0400, Tejun Heo wrote:
> 
> This patch defines CGROUP_WEIGHT_MIN/DFL/MAX to be used on all weight
> based control knobs and documents the conventions that controllers
> should follow on the unified hierarchy.  Except for io.weight knob,
> all existing unified hierarchy knobs are already compliant.  A
> follow-up patch will update io.weight.

> +- If a controller implements ratio based resource distribution, the
> +  control knob should be named "weight" and have the range [1, 10000]
> +  and 100 should be the default value.  The values are chosen to allow
> +  enough and symmetric bias in both directions while keeping it
> +  intuitive (the default is 100%).

Aside from 100% being a sane 'default', what it actually is is a unit.
100% == 1.

So I would suggest naming the thing CGROUP_WEIGHT_UNIT := 100,

> +/*
> + * All weight knobs on the default hierarhcy should use the following min,
> + * default and max values.  The default value is the logarithmic center of
> + * MIN and MAX and allows 100x to be expressed in both directions.
> + */
> +#define CGROUP_WEIGHT_MIN		1
> +#define CGROUP_WEIGHT_DFL		100
> +#define CGROUP_WEIGHT_MAX		10000

That said, I'm not entirely keen on having to change this.
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