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
--- 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");
