linux-kernel - Re: [RFC] maximum latency tracking infrastructure

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Message-Id: <1156493985.3032.13.camel@laptopd505.fenrus.org>
Date:	Fri, 25 Aug 2006 10:19:45 +0200
From:	Arjan van de Ven <arjan@...ux.intel.com>
To:	Matthew Garrett <mjg59@...f.ucam.org>
Cc:	linux-kernel@...r.kernel.org, len.brown@...el.com
Subject: Re: [RFC] maximum latency tracking infrastructure

On Thu, 2006-08-24 at 23:24 +0100, Matthew Garrett wrote:
> On Thu, Aug 24, 2006 at 07:41:35PM +0200, Arjan van de Ven wrote:
> 
> > +	/* the ipw2100 hardware really doesn't want power management delays
> > +	 * longer than 500usec
> > +	 */
> > +	modify_acceptable_latency("ipw2100", 500);
> > +
> 
> Hm. My BIOS claims that the C3 transition period is 85usec (and even my 
> C4 is 185) , but I've hit the error path where C3 gets disabled. Is this 
> really adequate? 

first of all that 500 is a bit of a guess on my side; James (the Intel
wireless guy) is on holiday so I couldn't get real numbers out of it.
But as proof of concept it's pretty ok :)

> Also, by the looks of it, the C3 disabling path is 
> still present - is it still theoretically necessary with the above, or 
> is this just a belt and braces approach?

the "problem" is that bioses lie about these numbers all the time as
well ;( (it's getting better but still).

Those numbers you gave, were those on batter or on AC ? (apparently for
the problem machines C3 latency goes WAY up when on battery, and then
the problem hits)
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