linux-kernel - Re: Battery class driver.

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Message-Id: <1161668623.10524.579.camel@localhost.localdomain>
Date:	Tue, 24 Oct 2006 15:43:42 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Matthew Garrett <mjg59@...f.ucam.org>
Cc:	Shem Multinymous <multinymous@...il.com>,
	David Zeuthen <davidz@...hat.com>,
	David Woodhouse <dwmw2@...radead.org>,
	linux-kernel@...r.kernel.org, olpc-dev@...top.org, greg@...ah.com,
	len.brown@...el.com, sfr@...b.auug.org.au
Subject: Re: Battery class driver.

On Tue, 2006-10-24 at 04:53 +0100, Matthew Garrett wrote:
> On Tue, Oct 24, 2006 at 01:48:27PM +1000, Benjamin Herrenschmidt wrote:
> > On Tue, 2006-10-24 at 04:27 +0100, Matthew Garrett wrote:
> 
> > > 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.
> 
> > I think it's up to the backend to poll more slowly and cache the results
> > on those machines then.
> 
> The kernel backend or the userspace backend? We need to decide on 
> terminology :) 

The kernel. Userspace don't have to know the details of how hard it is
for the backend to fetch the data imho.

> There's no good programmatic way of determining how long 
> a query will take other than doing it and looking at the result. I guess 
> we could do that at boot time.

Ben.


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