Subject: Re: Battery class driver.
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Matthew Garrett <mjg59@srcf.ucam.org>
Cc: Shem Multinymous <multinymous@gmail.com>,
       David Zeuthen <davidz@redhat.com>,
       David Woodhouse <dwmw2@infradead.org>, linux-kernel@vger.kernel.org,
       olpc-dev@laptop.org, greg@kroah.com, len.brown@intel.com,
       sfr@canb.auug.org.au
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Date: Tue, 24 Oct 2006 13:48:27 +1000
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On Tue, 2006-10-24 at 04:27 +0100, Matthew Garrett wrote:
> On Tue, Oct 24, 2006 at 04:56:30AM +0200, Shem Multinymous wrote:
> 
> > 30 seconds? I've seen battery applets that poll 1sec intervals (that's
> > actually useful when you tweak power saving). And for things like the
> > hdaps accelerometer driver, we're at the 50HZ region.
> 
> Reading the battery status has the potential to call an SMI that might 
> take an arbitrary period of time to return, and we found that having 
> querying at around the 1 second mark tended to result in noticable 
> system performace degredation.
> 
> Possibly it would be useful if the kernel could keep track of how long 
> certain queries take? That would let userspace calibrate itself without 
> having to worry about whether it was preempted or not.
> 
> > You can't require reading battery status to be a root-only operation.
> 
> We certainly can. Whether we want to is another matter :) I tend to 
> agree that moving to a setup that makes it harder for command-line users 
> to read the battery status would be a regression.

I think it's up to the backend to poll more slowly and cache the results
on those machines then.

Ben.


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