Re: kapmidled and AMD K6-2

From: Pavel Machek (
Date: Fri Oct 12 2001 - 08:01:39 EST


> > for the AMD K6-2 on a DFI motherboard AT/ATX, using the AT power supply,
> > this option is buggy. I mean the cycles kapmidled works doesn't cool the
> > processor, they hot him.
> Initially, I thought was odd. The spec seemed straight forward
> enough, and doesn't say we have to do any special magic.
> Just that "During the execution of the HLT instruction, the AMD-K6-2
> processor executes a Halt special cycle."
> The next bit is interesting however..
> "After BRDY# is sampled asserted during this cycle, and then EWBE#
> is also sampled asserted (if not masked off), the processor enters
> the halt state in which the processor disables most of its internal
> clock distribution."
> EWBE is a feature that is enabled with bits 2-3 of the EFER MSR.
> This controls the behaviour of the CPU with respect to ordering
> of write cycles. Behaviour here can affect performance, and from
> my interpretation of the above, the amount of power saving that
> is possible.
> You can control the EWBE register using powertweak
> (, but if you don't want to/are unable
> to build that, and want to do some further tests, let me know
> and I'll hack something up.

If I don't want to build powertweak, are you willing to hack something up
for me? ;-). [My k6-2 is too hot to slow down CPU fan. I tried throttling
it using ACPI, but no success. I want to cool it down so that fan slows
and machine becomes quiet.]

Philips Velo 1: 1"x4"x8", 300gram, 60, 12MB, 40bogomips, linux, mutt,
details at

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