Re: software CPU throttling on powerpc
Hello Hans,
On 23 Jan, this message from Hans Ekbrand echoed through cyberspace:
> I have an imac G3, which I want to use for a computing intensive task.
> I think this computer has a problem with overheating, because when it
> has been working for approximately 10 hours, it hangs.
>
> What I would like is to enforce some idle cycles which would prevent
> the CPU from overheating.
>
> On the ix86 processors, there is an thing called ACPI that has a
> function for this at /proc/acpi/processor/CPU0/throttling
>
> I *think* this is completely done in software (in the kernel, requires
> no hardware-support).
I don't know that feature, but if ACPI is involved, then it is unlikely
that it is in software.
> If that is the case, then it should be possible
> to do the same on the powerpc plattform, but I haven't found anything
> like that.
Have a look here:
http://www.cpu.lu/~mlan/linux/dev/g3upgrade.html
Quote:
"Since that means the processor is running too fast, I looked for a way
to slow it down. And I've found one.... The G3 processors implement a
feature which is designed for power saving and temperature control. It
works by slowing down the rate at which instructions are fetched from
the instruction cache. This is achieved by writing a non-zero value to
the ICTC special register in the G3 processor."
You might have to search for a way to control that register. Years ago I
had coded kernel support for /proc/sys/kernel/ictc to change that
register. Not sure it is in recent kernels; I have no G3 at hand to
check.
Cheers
Michel
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