Date: Tue, 15 Dec 2015 16:41:45 +0000
From: Mark Rutland <mark.rutland@arm.com>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: Juri Lelli <juri.lelli@arm.com>, peterz@infradead.org,
        Linus Walleij <linus.walleij@linaro.org>, will.deacon@arm.com,
        morten.rasmussen@arm.com, lorenzo.pieralisi@arm.com,
        vincent.guittot@linaro.org, linux-pm@vger.kernel.org,
        Chen-Yu Tsai <wens@csie.org>, devicetree@vger.kernel.org,
        Pawel Moll <pawel.moll@arm.com>,
        Ian Campbell <ijc+devicetree@hellion.org.uk>,
        Kumar Gala <galak@codeaurora.org>, Mark Brown <broonie@kernel.org>,
        Gregory CLEMENT <gregory.clement@free-electrons.com>,
        linux@arm.linux.org.uk, dietmar.eggemann@arm.com,
        linux-arm-kernel@lists.infradead.org,
        Thomas Petazzoni <thomas.petazzoni@free-electrons.com>,
        Paul Walmsley <paul@pwsan.com>, linux-kernel@vger.kernel.org,
        sudeep.holla@arm.com, Olof Johansson <olof@lixom.net>,
        Maxime Ripard <maxime.ripard@free-electrons.com>
Subject: Re: [RFC PATCH 2/8] Documentation: arm: define DT cpu capacity
 bindings
Message-ID: <20151215164145.GA8012@leverpostej>
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 <20151215154651.GK16007@e106622-lin>
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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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