PATCH: apm.c - runtime parameter for APM Idle call

PATCH: apm.c - runtime parameter for APM Idle call

[Borsenkow Andrej]

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After investigating kapm_idled problem here it turned out quite simple -
BIOS neither slows down CPU nor halts it so kapm_idled enters busy loop
doing basically

while !system_busy
  do nothing

eating away CPU. This applies to patch of Andreas as well.

I do not like an option of recompiling without CONFIG_APM_CPU_IDLE
because I think about distribution kernel in the first place. I have
ASUS CUSL2 motherboard - it is not unusual brand and obviously many
people have the same problem and you cannot expect all of them to
recompile kernel. So this patch adds runtime parameter (no-)apm-idle
that has the same effect - enabling/disabling usage of APM Idle BIOS
calls. It is initialised according to CONFIG_APM_CPU_IDLE and should be
100% compatible.

If Andreas patch is accepted it needs the same treatment.

I thought once about run-time detection - if BIOS reports that Idle does
not slow down CPU try Idle call once and compare jiffies (probably
repeat several times to be sure). Is it sensible?

Patch is agains 2.4.16-9.dk but should apply to any version I guess.

-andrej




[-- Attachment #2: apm-idle.diff --]
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--- arch/i386/kernel/apm.c.org	Sat Nov 10 00:58:02 2001
+++ arch/i386/kernel/apm.c	Sun Dec 16 21:23:27 2001
@@ -383,6 +383,11 @@
 static int			allow_ints;
 #endif
 static int			broken_psr;
+#ifdef CONFIG_APM_CPU_IDLE
+static int			apm_idle_enabled = 1;
+#else
+static int			apm_idle_enabled;
+#endif
 
 static DECLARE_WAIT_QUEUE_HEAD(apm_waitqueue);
 static DECLARE_WAIT_QUEUE_HEAD(apm_suspend_waitqueue);
@@ -1366,7 +1371,8 @@
 		 */
 		set_current_state(TASK_INTERRUPTIBLE);
 		apm_event_handler();
-#ifdef CONFIG_APM_CPU_IDLE
+		if (!apm_idle_enabled)
+			continue;
 		if (!system_idle())
 			continue;
 		
@@ -1393,7 +1399,6 @@
 			apm_event_handler();
 			timeout = 1;
 		}
-#endif
 	}
 	remove_wait_queue(&apm_waitqueue, &wait);
 }
@@ -1814,6 +1819,8 @@
 		if ((strncmp(str, "realmode-power-off", 18) == 0) ||
 		    (strncmp(str, "realmode_power_off", 18) == 0))
 			apm_info.realmode_power_off = !invert;
+		if (strncmp(str, "apm-idle", 8) == 0)
+			apm_idle_enabled = !invert;
 		str = strchr(str, ',');
 		if (str != NULL)
 			str += strspn(str, ", \t");

Re: PATCH: apm.c - runtime parameter for APM Idle call

[Dave Jones]

On 16 Dec 2001, Borsenkow Andrej wrote:

> I thought once about run-time detection - if BIOS reports that Idle does
> not slow down CPU try Idle call once and compare jiffies (probably
> repeat several times to be sure). Is it sensible?

A far simpler way would be to add DMI blacklist entries for the BIOSes
that don't do this, although this assumes the problem machine has a DMI
compliant BIOS.

Dave.

-- 
| Dave Jones.        http://www.codemonkey.org.uk
| SuSE Labs

PATCH: apm.c - detection of brokern APM Idle call implementation

[Borsenkow Andrej]

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On Пнд, 2001-12-17 at 06:34, Dave Jones wrote:
> On 16 Dec 2001, Borsenkow Andrej wrote:
> 
> > I thought once about run-time detection - if BIOS reports that Idle does
> > not slow down CPU try Idle call once and compare jiffies (probably
> > repeat several times to be sure). Is it sensible?
> 
> A far simpler way would be to add DMI blacklist entries for the BIOSes
> that don't do this, although this assumes the problem machine has a DMI
> compliant BIOS.
> 

Well, the following three-liners (+ comments) seems to do it. It checks
if clock was advanced after return from APM Idle - if not we assume BIOS
did not halt CPU and do it ourselves. The addidional condition &&
!current->need_resched is for the case when BIOS did halt CPU and
non-clock interrupt happened that waked up somebody else. But may be I
am just plain paranoid. The code has no impact for "BIOS slows CPU"
case.

It works here for broken BIOS. I appreciate if people with good BIOS
test it. 

-andrej


[-- Attachment #2: apm-idle-2.diff --]
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--- apm.c.bor	Tue Dec 18 20:30:08 2001
+++ apm.c	Tue Dec 18 20:42:24 2001
@@ -1381,13 +1381,18 @@
 		 */
 		if (apm_do_idle() != -1) {
 			unsigned long start = jiffies;
+			unsigned long before;
 			while ((!exit_kapmd) && system_idle()) {
-				if (apm_do_idle()) {
+				before = jiffies;
+				if (apm_do_idle() || (jiffies == before && !current->need_resched)) {
 					set_current_state(TASK_INTERRUPTIBLE);
 					/* APM needs us to snooze .. either
 					   the BIOS call failed (-1) or it
 					   slowed the clock (1). We sleep
-					   until it talks to us again */
+					   until it talks to us again.
+					   If clock did not advance CPU was
+					   not halted by BIOS so we do it
+					   now*/
 					schedule_timeout(1);
 				}
 				if ((jiffies - start) > APM_CHECK_TIMEOUT) {