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Subjectlinux-2.6.0-test2: Never using pm_idle (CPU wasting power)
Hi,

on a Thinkpad 600X I noticed the CPU getting very hot. It turned
out that pm_idle was never called (which invokes the ACPI pm_idle
call in this case) and default_idle was used instead.

/* arch/i386/kernel/process.c, line 723 */
void cpu_idle (void)
{
/* endless idle loop with no priority at all */
while (1) {
void (*idle)(void) = pm_idle;
if (!idle)
idle = default_idle; /* once on bootup */
irq_stat[smp_processor_id()].idle_timestamp = jiffies;
while (!need_resched())
idle();
schedule(); /* never reached */
}
}

The schedule() is never reached (need_resched() is never 0) and
so the idle-variable is not updated. pm_idle is NULL on the
first call to cpu_idle on this thinkpad, and so I stay idling
in the default_idle()-function.

By moving the "void *idle = pm_idle; if(!idle)..." in the inner
while()-loop the notebook calls pm_idle (as it get's updated by ACPI)
and stays cool.

Chris

--
Programming today is a race between software engineers striving to build
bigger and better idiot-proof programs, and the Universe trying to
produce bigger and better idiots. So far, the Universe is winning.
-- Rich Cook
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