Re: 2.6.12-mm1 boot failure on NUMA box.

["Martin J. Bligh" <Martin.Bligh@us.ibm.com>]

--On Friday, June 24, 2005 21:52:48 +0200 Ingo Molnar <mingo@elte.hu> wrote:

> 
> * Martin J. Bligh <mbligh@mbligh.org> wrote:
> 
>> > -	/*
>> > -	 * 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.
> 
> is the only problem the unsyncedness? That should be fine as far as the 
> scheduler is concerned. (we compensate for per-CPU drifts)

Well, I think so. But I don't see how you're going to compensate for
large-scale unsynced-ness safely. I've always completely avoided the
TSC altogether on NUMA-Q ... would prefer to keep it that way. We got
lots of wierd random crashes, panics, hangs, and -ve time offsets 
returned from userspace time commands last time I tried it.

M.

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