linux-kernel - Re: [PATCH v2 2/3] PM / DEVFREQ: add example governors

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Message-Id: <201105182146.51869.rjw@sisk.pl>
Date:	Wed, 18 May 2011 21:46:51 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	myungjoo.ham@...il.com
Cc:	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	"Greg Kroah-Hartman" <gregkh@...e.de>,
	Mark Brown <broonie@...ena.org.uk>,
	Jiejing Zhang <kzjeef@...il.com>, Pavel Machek <pavel@....cz>,
	Colin Cross <ccross@...gle.com>, Nishanth Menon <nm@...com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Len Brown <len.brown@...el.com>,
	Kyungmin Park <kyungmin.park@...sung.com>
Subject: Re: [PATCH v2 2/3] PM / DEVFREQ: add example governors

On Wednesday, May 18, 2011, MyungJoo Ham wrote:
> 2011/5/18 Rafael J. Wysocki <rjw@...k.pl>:
> > On Wednesday, May 11, 2011, MyungJoo Ham wrote:
> >> Three CPUFREQ-like governors are provided as examples.
> >>
> >> powersave: use the lowest frequency possible. The user (device) should
> >> set the polling_ms as 0 because polling is useless for this governor.
> >>
> >> performance: use the highest freqeuncy possible. The user (device)
> >> should set the polling_ms as 0 because polling is useless for this
> >> governor.
> >>
> >> simple_ondemand: simplified version of CPUFREQ's ONDEMAND governor.
> >>
> >> When a user updates OPP entries (enable/disable/add), OPP framework
> >> automatically notifies DEVFREQ to update operating frequency
> >> accordingly. Thus, DEVFREQ users (device drivers) do not need to update
> >> DEVFREQ manually with OPP entry updates or set polling_ms for powersave
> >> , performance, or any other "static" governors.
> >
> > Well, do you expect anyone to actually use them?  If not, it would make
> > more sense to put them into a doc.
> 
> According to our experiences of DVFS(although this "DEVFREQ" is not
> applied to them, yet) in memory-bus and GPU,
> I expect most DEVFREQ users might use "simple_ondemand" and
> expect "powersave" and "performance" will probably mostly used while
> testing and debugging.
> ("userspace"-like governor would be also useful for that purpose, but
> I'd add it later)

It would be good to have at least one in-tree user for each of them
(not necessarily from the start, but at one point in the future at least).

So if you have any _specific_ users in mind, please let me know.

Thanks,
Rafael
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