Re: [parisc-linux] different PA2.0 CPUs in the same box?

[Grant Grundler <grundler@cup.hp.com>]

Grant Grundler wrote:
> Alex deVries wrote:
> > 
> > Can you mix and match different PA2.0 CPUs in a multiprocessor box?
> > An 8000 and an 8200?  
> 
> And HP hasn't mix/matched processor clock frequency's in one box either.
> 870 (4-way/PA1.0/CIO) I think had something funny about the clocks which
> I think was repeated in the T-class and possible planned in newer
> architectures. Can anyone shed more light on this?

I think I remember the problem now.

The processors can run from a "system clock" and they all run synchronous.
No chance of "clock drift" since they run at exactly the same pace.
But on systems like 870, T-class and N-class, the processors are fed clock
signals from (similar but) different sources.  Each frequency domain will
slowly drift from the "average" and thus the processor clocks need to be
resyncronized regularly.

> Minimizing clock drift of the various processors in an SMP box is
> a difficult problem. Keeping accurate time is important but
> synchronization of processors too often can really hurt performance.

grant