Re: kapm-idled Funny in 2.4.10-ac12?

From: Alan Cox (
Date: Fri Oct 12 2001 - 13:08:52 EST

> I am having almost the same problem in 2.4.12-ac1:
> gallir@linux:~$ uname -a
> Linux linux 2.4.12-ac1 #2 Fri Oct 12 19:01:03 CEST 2001 i686 unknown
> kapm-idled consumes a 14% of CPU (in a P3 1GHz)
> 3 root 17 0 0 0 0 RW 14.3 0.0 1:17 kapm-idled
> The same happens with vanilla Linus tree (tested up to 2.4.11). In a P2,
> CPU consuption was more than 85%.
> The CPU's temperature, while the system idle, is more than 4 degrees (C)
> higher than the same conditions with the kapm-idled disabled.

I've been reading throught the APM spec and code a bit further. The more
I read the more I wonder quite how our idle code is meant to work and what
kind of beer was overconsumed during its writing.

There are two glaring issues I can see right now

#1 The BIOS might sleep for a tick, but it is also is allowed to slow
        the cpu and return straight back to us.

        If it returns back to us we spin in a tight loop at the lower clock
        speed calling the APM bios. Not ideal.

        Just fixed that in my tree for the next -ac

#2 We test system_idle() nr_running==1, but we spent all our time
        pretending we aren't running. Im not 100% sure the test is safe

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