linux-2.6.0-test2: Never using pm_idle (CPU wasting power)

From: Christian Vogel (
Date: Thu Jul 31 2003 - 08:07:22 EST


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())
                        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.


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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This archive was generated by hypermail 2b29 : Thu Jul 31 2003 - 22:00:49 EST