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

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Message-ID: <20150804145353.GC17598@mtj.duckdns.org>
Date:	Tue, 4 Aug 2015 10:53:53 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Peter Zijlstra <peterz@...radead.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

Hello, Peter.

On Tue, Aug 04, 2015 at 10:48:55AM +0200, Peter Zijlstra wrote:
> > +- 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,

It's a minor point either way but I think people would generally find
default more familiar.

> > +/*
> > + * 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.

Yeah, changing the scale is an icky thing to do but I think the
benefits of unifying the scales across different controllers outweigh
here.

Thanks.

-- 
tejun
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