Re: APM driver patch summary

From: Borsenkow Andrej (
Date: Fri Jan 04 2002 - 14:56:18 EST

Sorry for the delay, I was off before New Year and then could not test
it ...

On , 2001-12-22 at 17:44, Andreas Steinmetz wrote:
> Hi,
> I merged 2., 3. and 4. (attached) with some modifications.
> 1. There is now a module parameter apm-idle-threshold which allows to override
> the compiled in idle percentage threshold above which BIOS idle calls are
> done.
> 2. I modified Andrej's mechanism to detect a defunct BIOS (stating 'does stop
> CPU' when it actually doesn't) to take into account that there's other
> interrupts than the timer interrupt that could reactivate the cpu.
> As there's 16 hardware interrupts on x86 (apm is arch specific anyway) I do
> use a leaky bucket counter for a maximum of 16 idle rounds until jiffies is
> increased. When the counter reaches zero it stays at this value and the
> system idle routine is called. If BIOS idle is a noop then the counter
> reaches zero fast, thus effectively halting the cpu.

I do not think you need it. Either interrupt waked up somebody and set
need_resched and we exit loop or nobody is ready to run and we can sleep
again. Why complicate things any more than needed?

> Andrej, could you please test the patch if it works for your laptop?

It does not work and I am very surprised it works for somebody (well,
there are conditios when it will work). By default pm_idle is always
NULL so we *never* actually call kernel function that really stops CPU.
Main idle task is cpu_idle that does

if (pm_idle)

and CPU is halted in default_idle. So your patch just enters busy loop
calling BIOS APM Idle over and over again just like it was before.

Attached patch makes apm_cpu_idle do the same and call either old
pm_idle (a.k.a. sys_idle) or default_idle. I removed your interrupt
handling - it does not actually affect the problem but it still is not
needed IMHO. t1, t2 are changed from int into long because jiffies is
long - not sure if it is really needed.

cheers and sorry for delay


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