linux-kernel - Re: [PATCH v2 3/6] PowerCap: Added to drivers build

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Date:	Mon, 07 Oct 2013 08:46:26 -0700
From:	Arjan van de Ven <arjan@...ux.intel.com>
To:	Gene Heskett <gheskett@...v.com>
CC:	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	"Brown, Len" <len.brown@...el.com>,
	Jacob Pan <jacob.jun.pan@...ux.intel.com>,
	Linux PM list <linux-pm@...r.kernel.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Greg KH <gregkh@...uxfoundation.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>
Subject: Re: [PATCH v2 3/6] PowerCap: Added to drivers build

On 10/6/2013 1:15 PM, Gene Heskett wrote:
>> and if you wonder what linux does today without the framework; there are
>> mechanisms that kick in at the very end of the range, that are very
>> draconian like taking the 3.0Ghz processor down to effectively 100MHz,
>> or even a system reboot. The point of what Jacob and Srinivas are trying
>> to add is to intervene slightly earlier (these failsafe mechanisms are
>> still there) but much much more gently.
>
> First off, we are not using the type of boards for controllers that would
> burn anything up sans its normal cooling, which is entirely passive on an
> atom powered board as you well know.  So there is no fan to fail and start
> your doomsday scenario in abut 30% of the cases now, but there are a rather
> dukes mixture of other boards being used yet.  Those will be replaced in
> due time as they fail, or the IRQ latency finally starts costing the shop
> owner money because the machine can't be run at the optimum speed with that
> poorly architect-ed board, probably with Atoms or BBB's.

so if your system today never hits the thermal shutdown...
... you're not going to hit anything powercapping either.



> If you insist on doing this, in the face of ample evidence its nothing but
> a feel good action on your part, then the least we ask is for a tally
> signal output, far enough in advance, say 0.25 seconds, to do a graceful,

btw one thing to note that this is just the kernel mechanism; the actual
knobs that it provides get turned by some userspace daemon..
I would fully expect that if you even ship such a daemon on your realtime device,
that you build in the notification for sure.


> In fact, I'd go so far as to say that any hardware capable of self-
> destructing in normal operation, does not need to guarded by this proposed
> function, but blacklisted instead, it is patently a defective design from
> square one regardless of the brand name on the box.  Or just let it burn
> up, the warranty returns will educate the maker/designer soon enough.

self-destruct or reboot... either case you will not like it.


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