linux-kernel - Re: [PATCH 2/9] x86 idle: remove NOP cpuinfo_x86.hlt_works

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Message-ID: <4D949918.8010109@zytor.com>
Date:	Thu, 31 Mar 2011 08:09:12 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	Ingo Molnar <mingo@...e.hu>, Len Brown <lenb@...nel.org>,
	x86@...nel.org, linux-kernel@...r.kernel.org,
	linux-pm@...ts.linux-foundation.org,
	Len Brown <len.brown@...el.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 2/9] x86 idle: remove NOP cpuinfo_x86.hlt_works_ok flag

On 03/31/2011 07:41 AM, Alan Cox wrote:
>>
>> What it was was bad power supplies or low-capacitance, high-inductance
>> power distribution that happened to work with MS-DOS which always burned
>> the CPU at 100% and therefore left the power draw relatively consistent
>> current.  A proper OS putting the CPU in HLT produced a lot more high
>> frequency noise on the power busses, with disastrous results without
>> proper bypass.
> 
> And also chipset errata in some cases - eg some revisions of the CS5510
> hung the box solid if a CPU hlt occurred during an IDE transfer. I don't
> think any CS5510s are still around although I've had mail from someone
> with a CS5520 in use not that long ago so who knows!
> 
> The joy of ancient history.

Ah, yes, I guess there was a special cycle on the bus which the chipset
could misinterpret.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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