linux-kernel - Re: Linux 2.6.30-rc8 [also: VIA Support]

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Date:	Sat, 6 Jun 2009 07:17:44 -0500
From:	"Michael S. Zick" <lkml@...ethan.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Duane Griffin <duaneg@...da.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Harald Welte <HaraldWelte@...tech.com>
Subject: Re: Linux 2.6.30-rc8 [also: VIA Support]

On Thu June 4 2009, Linus Torvalds wrote:
> 
> On Thu, 4 Jun 2009, Michael S. Zick wrote:
> >
> > Yes, I build test cases with and without - -
> > It was a fixed-speed kernel build that first hit the 4 hour up-time mark.
> > I just reposted that build today (the -09143lk).
> > 
> > > Features like that easily put a huge stress on power regulators etc, if 
> > > they result in sudden changes in current draw.  Underspecced capacitors 
> > > etc can cause CPU "brown-outs", which in turn can easily cause total 
> > > failure. 
> > 
> > There is also a possible thermal issue with these machines - -
> > I doubt that VIA runs their qualification testing in bake ovens;
> > which is what NetBook cases amount too.  ;)
> 
> If the fixed-speed case runs for longer, it's not likely to be a thermal 
> issue. The fixed speed case should be the higher-power one.
> 

I can respond to that point now; VIA Tech has answered some of my questions -

The mainstream kernel, e_powersaver, is *under-clocking* my machine -

The cpuid instruction provides the minimum and maximum GSF values 
(Guaranteed Stable Frequency) for that processor mask run -
Passing that on as the lower and upper limits to e_powersaver should
stop that problem.  Will be testing this RSN.

Once you start operating the processor outside of the reported-by-silicon mask
limits - quote: "there is no quarantee of stable operation" - -

To that I add my opinion:
For a severely under-clocked machine (already possibly un-stable) - -
Thermal effects are almost certain to be present.
 
To paraphrase VIA Tech once again: "Don't do that."  ;)

Mike
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