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Reduced the number of processes used by default when testing. - #2888
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I don't think it is a fluke that there are not TimeoutExceptions here... 🎉 |
| self.num_processors = multiprocessing.cpu_count() - 1 | ||
| # Choose a magic number that works reasonably well for the default | ||
| # number of processes. | ||
| self.num_processors = (multiprocessing.cpu_count() + 1) // 4 + 1 |
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@pelson What's the logic behind this lovely piece of maths?
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It's a magic number... there is no solid/defensible logic other than:
- It should be at least one
- It shouldn't fill all CPUs if there are lots of them
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Given we are far more parallelised now in iris (thanks to our new-found dask abilities) we don't need to use as many processes in parallel when testing. I didn't do any particularly sophisticated analysis of the "sweet spot", but leave that as an exercise for the interested reader...
In summary: we don't need to flood the machine with processes, and anything is better than what we currently do...
On Travis (where the numbers are extremely erratic), using 8 processes appears to take a similar amount of time to using 3. On my laptop (4 core), using 1 process takes about the same amount of time as 3.