Re: 2.6.2: P4 ClockMod speed

From: Dominik Brodowski <linux@dominikbrodowski.de>
To: dual_bereta_r0x <dual_bereta_r0x@arenanetwork.com.br>,
	Pavel Machek <pavel@ucw.cz>
Cc: cpufreq@www.linux.org.uk
Subject: Re: 2.6.2: P4 ClockMod speed
Date: Sun, 14 Mar 2004 15:44:02 +0100	[thread overview]
Message-ID: <20040314144402.GA22268@dominikbrodowski.de> (raw)
In-Reply-To: <20040225174326.GD1214@elf.ucw.cz> <403D4BD3.7050703@arenanetwork.com.br>

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On Thu, Feb 26, 2004 at 01:28:51AM +0000, dual_bereta_r0x wrote:
> In x86 world, this info is wrong. The *multiplier* is locked inside 
> processor (Intel P4) or by some "dips" on cpu core (AMD Athlon XP) -- 
> unless you have such as "enginering samples", with didn't have this lock 
> --, but front-side-bus is changeable via MoBo BIOS.

Depends...

> Also, if you just 
> add 0.5v in your CPU you can made it running faster than designed. The 
> same applies to memory. That's why we bought DDR533 mems to run in 
> DDR400 hardwares. We increase FSB and our mems could run with this new FSB.
> 
> Again, showing *max* from manufacturer instead of *actual* speed is 
> wrong. Even if the machine has or not capabilities to run with more/less 
> power than it has designed for, is not up to the OS decide it. The OS 
> should run or not,

The OS runs, the p4-clockmod driver runs, so that is besides the point here.

> but the user has chosen this path; it must only tell 
> him what's *really* happening. "Your actual clock differs from 
> manufacturer. Its *your* fault if any component fail or 
> malfunctions/bugs arrives because of this."

The problem is that cpu_khz is partly unreliable, partly not available, so
there's no reliable way to detect _actual_ CPU speed for the p4-clockmod
driver. Also, there's the need to warn users about the lack of usefullness
of the p4-clockmod driver in the very most cases, and to avoid code
duplication the speedstep_detect function is used. Then we get the
_reliable_ detection of "specification speed", which is in most cases equal
to the "actual speed", almost for free.

On Wed, Feb 25, 2004 at 06:43:27PM +0100, Pavel Machek wrote:
> Hey, that's ugly. Values should be real.

Indeed. But if they're not known (and cpu_khz _is_ unreliable), what should
be done?

	Dominik

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