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

[H. Peter Anvin]

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.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/