Re: 2.6.12-mm1 boot failure on NUMA box.

[Martin J. Bligh]

>> OK, still broken with the last 3 backed out, but works with the last 4 
>> backed out. So I guess it's scheduler-cache-hot-autodetect.patch that 
>> breaks it. Con just sent me something else to try to fix it in order 
>> to run next ... will do that.
> 
> hm. Does it work if you disable migration-autodetect via passing in e.g.  
> migration_cost=1000,2000,3000 on the boot line? Is it perhaps the 
> excessive debugging that hurts.
> 
> or does it work if you undo the chunk below? Seemed harmless, but has 
> CONFIG_NUMA relevance.
> 
> 	Ingo
> 
> --- linux/arch/i386/kernel/timers/timer_tsc.c.orig
> +++ linux/arch/i386/kernel/timers/timer_tsc.c
> @@ -133,18 +133,15 @@ static unsigned long long monotonic_cloc
>  
>  /*
>   * Scheduler clock - returns current time in nanosec units.
> + *
> + * it's not a problem if the TSC is unsynchronized,
> + * as the scheduler will carefully compensate for it.
>   */
>  unsigned long long sched_clock(void)
>  {
>  	unsigned long long this_offset;
>  
> -	/*
> -	 * In the NUMA case we dont use the TSC as they are not
> -	 * synchronized across all CPUs.
> -	 */
> -#ifndef CONFIG_NUMA
> -	if (!use_tsc)
> -#endif
> +	if (!cpu_has_tsc)
>  		/* no locking but a rare wrong value is not a big deal */
>  		return jiffies_64 * (1000000000 / HZ);

Humpf. That does look dangerous on a NUMA-Q. The TSCs aren't synced,
and we can't use them .... have to use PIT, whether the CPUs have TSC
or not.

M.
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