linux-kernel - Re: [PATCH] regulator: notify sysfs when voltage is set

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Date:	Thu, 15 Mar 2012 23:26:58 +0900
From:	Simon Horman <horms@...ge.net.au>
To:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
Cc:	Liam Girdwood <lrg@...com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] regulator: notify sysfs when voltage is set

On Thu, Mar 15, 2012 at 12:46:31PM +0000, Mark Brown wrote:
> On Thu, Mar 15, 2012 at 09:04:33PM +0900, Simon Horman wrote:
> 
> > This allows libudev to be used to monitor voltage changes and thus allows
> > user-space code to avoid polling the sysfs entry for changes.
> 
> I notice that we don't generate similar events for cpufreq...  what are
> the performance implications from firing off udev (which isn't free)
> every time we scale the CPU frequency?  It feels like this might be
> disruptive, especially with a governor like ondemand which responds to
> system load.

Hi Mark,

that is a good point and to be honest not one that I had considered.  For
the use-case that I have in mind, which is basically to log voltage changes
over time, it may be acceptable to rate-limit notifications somehow. But at
that point I may be better off just polling.

Out of interest, how often can ondemand potentially change the voltage?
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