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PERF: Use Boost.SmallVec in BCO interpolator

Laurențiu Nicola requested to merge bco-small-vec into develop

Summary

Use a small vector container for the output pixel and interpolator coefficients in BCOInterpolateImageFunction.

Rationale

This avoids two (for scalar images) or three (for vector ones) for small interpolation radii and number of bands.

before:
286.76user 5.17system 0:36.00elapsed 810%CPU (0avgtext+0avgdata 1013876maxresident)k
2288inputs+15071432outputs (5major+1442780minor)pagefaults 0swaps
290.62user 5.28system 0:34.09elapsed 867%CPU (0avgtext+0avgdata 1013312maxresident)k
35776inputs+15071432outputs (207major+1443014minor)pagefaults 0swaps
291.82user 5.01system 0:34.05elapsed 871%CPU (0avgtext+0avgdata 1013196maxresident)k
18960inputs+15071432outputs (133major+1443078minor)pagefaults 0swaps

after:
260.86user 5.44system 0:37.12elapsed 717%CPU (0avgtext+0avgdata 1013652maxresident)k
4272inputs+15071432outputs (3major+1443217minor)pagefaults 0swaps
257.90user 5.85system 0:38.22elapsed 690%CPU (0avgtext+0avgdata 1014272maxresident)k
8inputs+15071432outputs (1major+1443207minor)pagefaults 0swaps
261.12user 5.58system 0:36.90elapsed 722%CPU (0avgtext+0avgdata 1012968maxresident)k
0inputs+15071432outputs (0major+1443212minor)pagefaults 0swaps

Tested on Ubuntu 18.04. I expect it might make a larger difference on older systems, because the GLIBC memory allocator used to be very slow (it got a per-thread cache in 2.26).

Implementation Details

I'm not sure what's the minimum Boost version we support, so I left in a path for pre-1.58, where small_vector is not available.

Additional notes

This is technically a breaking change:

  • the BCOInterpolateImageFunctionBase::CoefContainer type is public and its type has changed
  • BCOInterpolateImageFunctionBase::EvaluateCoef is no longer virtual

Copyright

The copyright owner is Laurențiu Nicola / CS ROMANIA and has signed the ORFEO ToolBox Contributor License Agreement.

Check before merging:

  • All discussions are resolved
  • At least 2 👍 votes from core developers, no 👎 vote.
  • The feature branch is (reasonably) up-to-date with the base branch
  • Dashboard is green
  • Copyright owner has signed the ORFEO ToolBox Contributor License Agreement
  • Optionally, run git diff develop... -U0 --no-color | clang-format-diff.py -p1 -i on latest changes and commit
Edited by Laurențiu Nicola

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