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
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
On ???, 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