[Insight-developers] non-deterministic v4 registrations in 4.5.x

[Simon Alexander]

I've been finding some regressions in registration results when using
systems with different numbers of cores (so the thread count is different).
 This is resolved by fixing the global max.

It's difficult for me to run the identical code on against 4.4.2, but
similar experiments were run in that timeframe without these regressions.

I recall that there were changes affecting multhreading in the v4
registration in 4.5.0 release, so I thought this might be a side effect.

So a few questions:

Is this behaviour expected?

Am I correct that this was not the behaviour in 4.4.x ?

Does anyone who has a feel for  the recent changes 4.4.2 -> 4.5.[0,1]  have
a good idea where to start looking?  I haven't yet dug into the
multithreading architecture, but this "smells" like a data partitioning
issue to me.

Any other thoughts?

cheers,
Simon
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