linux-kernel - Re: [RFC PATCH 2/8] Documentation: arm: define DT cpu capacity bindings

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Message-ID: <20151215164145.GA8012@leverpostej>
Date:	Tue, 15 Dec 2015 16:41:45 +0000
From:	Mark Rutland <mark.rutland@....com>
To:	Catalin Marinas <catalin.marinas@....com>
Cc:	Juri Lelli <juri.lelli@....com>, peterz@...radead.org,
	Linus Walleij <linus.walleij@...aro.org>, will.deacon@....com,
	morten.rasmussen@....com, lorenzo.pieralisi@....com,
	vincent.guittot@...aro.org, linux-pm@...r.kernel.org,
	Chen-Yu Tsai <wens@...e.org>, devicetree@...r.kernel.org,
	Pawel Moll <pawel.moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Mark Brown <broonie@...nel.org>,
	Gregory CLEMENT <gregory.clement@...e-electrons.com>,
	linux@....linux.org.uk, dietmar.eggemann@....com,
	linux-arm-kernel@...ts.infradead.org,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Paul Walmsley <paul@...an.com>, linux-kernel@...r.kernel.org,
	sudeep.holla@....com, Olof Johansson <olof@...om.net>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>
Subject: Re: [RFC PATCH 2/8] Documentation: arm: define DT cpu capacity
 bindings

On Tue, Dec 15, 2015 at 04:23:18PM +0000, Catalin Marinas wrote:
> On Tue, Dec 15, 2015 at 03:57:37PM +0000, Mark Rutland wrote:
> > On Tue, Dec 15, 2015 at 03:46:51PM +0000, Juri Lelli wrote:
> > > On 15/12/15 15:32, Mark Rutland wrote:
> > > > On Tue, Dec 15, 2015 at 03:08:13PM +0000, Mark Brown wrote:
> > > > > My expectation is that we just need good enough, not perfect, and that
> > > > > seems to match what Juri is saying about the expectation that most of
> > > > > the fine tuning is done via other knobs.
> > > > 
> > > > My expectation is that if a ballpark figure is good enough, it should be
> > > > possible to implement something trivial like bogomips / loop_per_jiffy
> > > > calculation.
> > > 
> > > I didn't really followed that, so I might be wrong here, but isn't
> > > already happened a discussion about how we want/like to stop exposing
> > > bogomips info or rely on it for anything but in kernel delay loops?
> > 
> > I meant that we could have a benchmark of that level of complexity,
> > rather than those specific values.
> 
> Or we could simply let user space use whatever benchmarks or hard-coded
> values it wants and set the capacity via sysfs (during boot). By
> default, the kernel would assume all CPUs equal.

I assume that a userspace override would be available regardless of
whatever mechanism the kernel uses to determine relative
performance/effinciency.

I am not opposed to that mechanism being "assume equal".

Mark.
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