Re: [RFC patch 15/15] LTTng timestamp x86

[Bjorn Helgaas]

On Monday 20 October 2008 04:29:07 pm H. Peter Anvin wrote:
> Linus Torvalds wrote:
> > 
> > But it's not going to solve the "hey, I have 512 CPU's, they are all on 
> > different boards, and no, they are _not_ synchronized to one global 
> > clock!".
> > 
> > That's why I'd suggest making _purely_ local time, and then aiming for 
> > something NTP-like. But maybe there are better solutions out there.
> 
> At the same time, it would definitely be nice to encourage vendors of 
> large SMP systems to provide a common root crystal (frequency standard) 
> for a single SMP domain.  Preferrably a really good one, TCXO or better.

A single root crystal is nice for us software guys.  But it often
also turns into a single point of failure, which the hardware guys
are always trying to eliminate.  So I think multiple crystals are
inevitable for the really large machines.

Bjorn
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