Re: kapm-idled shows 90+% cpu usage when idle

Mikael Pettersson (mikpe@csd.uu.se)
Fri, 10 Aug 2001 02:36:50 +0200 (MET DST)


On Thu, 9 Aug 2001 19:33:42 -0400, safemode <safemode@speakeasy.net> wrote:
>Is this a true usage reading or just some quirk that's supposed to happen?
>I really doubt that this kernel daemon should really be using cpu. It seems
>to respond with a higher cpu usage when i'm idle. It immediately goes away
>when something else uses cpu. If you need any more info just ask. I'm

Do you have CONFIG_APM_CPU_IDLE=y in your .config? If so, disable it.

There was a thread about this problem some months ago. I found
that on all of my APM-capable machines, including a Dell laptop,
CONFIG_APM_CPU_IDLE=y had a negative effect. The kernel ended up
in a tight loop performing tons of APM IDLE BIOS calls, since each
BIOS call returned immediately without having idled the CPU.

Leaving CONFIG_APM_CPU_IDLE unset lets the kernel use its own
"HLT when idle" code. On my main development box, idle CPU
temperature dropped >10 degrees C, and kapm-idled now uses 0% CPU.

/Mikael
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