Messages in this thread Patch in this message | | | Date | Thu, 31 Jul 2003 15:59:48 -0700 | From | Andrew Morton <> | Subject | Re: linux-2.6.0-test2: Never using pm_idle (CPU wasting power) |
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Christian Vogel <vogel@skunk.physik.uni-erlangen.de> wrote: > > 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.
Yes, I assume that need_resched() is always false because kernel preemption cuts in first. Can you please confirm that you're using CONFIG_PREEMPT, and that the problem goes away if CONFIG_PREEMPT is disabled?
The problem which you identify will also invalidate the idle_timestamp instrumentation so I think we should move that inside as well.
diff -puN arch/i386/kernel/process.c~acpi-idle-fix arch/i386/kernel/process.c --- 25/arch/i386/kernel/process.c~acpi-idle-fix Thu Jul 31 15:51:16 2003 +++ 25-akpm/arch/i386/kernel/process.c Thu Jul 31 15:57:27 2003 @@ -139,12 +139,15 @@ void cpu_idle (void) { /* endless idle loop with no priority at all */ while (1) { - void (*idle)(void) = pm_idle; - if (!idle) - idle = default_idle; - irq_stat[smp_processor_id()].idle_timestamp = jiffies; - while (!need_resched()) + while (!need_resched()) { + void (*idle)(void) = pm_idle; + + if (!idle) + idle = default_idle; + + irq_stat[smp_processor_id()].idle_timestamp = jiffies; idle(); + } schedule(); } } _
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