Re: [PATCH 01/16] math128: Introduce various 128bit primitives

[Peter Zijlstra]

On Fri, 2012-10-26 at 11:24 +0200, Ingo Molnar wrote:

> So can we control this by restricting the users and avoiding the 
> overflow?
> 
> A 2^64 result should be a *huge* amount of space already for 
> just about anything.

I _think_ something like: dl_runtime * dl_deadline < U64_MAX, might do
that. The question is, is this constraint usable? Simplified that boils
down to about 4 seconds each, which sounds pretty much ok for most
people -- but such statements usually come back to bite you (640kb
anybody...).

Hmm, patch 8 (which adds period support) changes this slightly again.
Would it then end up being something like:

  dl_period * dl_runtime < U64_MAX && dl_deadline * dl_runtime < U64_MAX

?

Juri, did I get that constraint right and do you know about use-cases
where this would be prohibitive?

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