Re: [PATCH 2/9] x86 idle: remove NOP cpuinfo_x86.hlt_works_ok flag

From: H. Peter Anvin
Date: Thu Mar 31 2011 - 10:20:38 EST


On 03/31/2011 02:35 AM, Ingo Molnar wrote:
>
> * Alan Cox <alan@xxxxxxxxxxxxxxxxxxx> wrote:
>
>>> Btw., we used to auto-detect broken HLT systems IIRC - but that got lost
>>> already. We should at least honor the boot parameter.
>>
>> I don't believe we ever auto detected them or found a way to do so. That
>> was why the HLT message was printed before hlt was executed.
>
> Yeah - the CPU hang was unrecoverably deep so no auto-detection was possible.
>
> That's seriously ancient stuff - still, keeping the boot option around (<10
> lines of code) does not hurt anyone.
>

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.

-hpa

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

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