Re: APM driver patch summary

Borsenkow Andrej
2002-01-04T19:56:52Z

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

On Сбт, 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)
pm_idle()
or
default_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

-andrej

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--- linux-2.4.16-9mdk/arch/i386/kernel/apm.c.combined Sun Dec 23 22:15:43 2001
+++ linux-2.4.16-9mdk/arch/i386/kernel/apm.c Fri Jan 4 22:26:09 2002
@@ -761,6 +761,7 @@
static void (*sys_idle)(void);
static unsigned int last_jiffies = 0;
static unsigned int last_stime = 0;
+extern void default_idle(void);

/**
* apm_cpu_idle - cpu idling for APM capable Linux
@@ -774,8 +775,8 @@
{
static int use_apm_idle = 0;
int apm_is_idle = 0;
- unsigned int t1 = jiffies - last_jiffies;
- unsigned int t2;
+ unsigned long t1 = jiffies - last_jiffies;
+ unsigned long t2;

recalc: if(t1 > IDLE_CALC_LIMIT)
goto reset;
@@ -799,15 +800,8 @@
t1 = jiffies;
switch (apm_do_idle()) {
case 0: apm_is_idle = 1;
- if (t1 != jiffies) {
- if (t2) {
- t2 = IDLE_LEAKY_MAX;
- continue;
- }
- } else if (t2) {
- t2--;
+ if (t1 != jiffies)
continue;
- }
break;
case 1: apm_is_idle = 1;
break;
@@ -816,6 +810,8 @@

if (sys_idle)
sys_idle();
+ else
+ default_idle();

t1 = jiffies - last_jiffies;
if (t1 > HARD_IDLE_TIMEOUT)
--- linux-2.4.16-9mdk/arch/i386/kernel/process.c.org Thu Dec 13 13:12:46 2001
+++ linux-2.4.16-9mdk/arch/i386/kernel/process.c Fri Jan 4 22:24:47 2002
@@ -77,8 +77,10 @@
/*
* We use this if we don't have any better
* idle routine..
+ * It is also called from apm_cpu_idle if BIOS does not stop clock
+ * for us
*/
-static void default_idle(void)
+void default_idle(void)
{
if (current_cpu_data.hlt_works_ok && !hlt_counter) {
__cli();