Performance Shift(s): `9192442a`

[github-actions]

Benchmark comparison has identified performance shifts at

• commit 9192442 ([CI Bot] environment lockfiles auto-update #5177).

Please review the report below and take corrective/congratulatory action as appropriate 🙂

Performance shift report

       before           after         ratio
     [21b8a2cd]       [9192442a]
     <main~1>         <main>    
+      44.3±0.7ms       55.9±0.9ms     1.26  experimental.ugrid.Mesh.time_eq(6)
+      10.1±0.4ms       13.6±0.3ms     1.34  experimental.ugrid.MeshCoordLazy.time_bounds(10000)
+      8.80±0.2ms       11.7±0.2ms     1.33  experimental.ugrid.MeshCoordLazy.time_bounds(6)
+      3.63±0.2ms       5.39±0.1ms     1.48  experimental.ugrid.MeshCoordLazy.time_points(10000)
+      7.36±0.2ms       10.8±0.2ms     1.46  experimental.ugrid.MeshCoordLazy.time_points(1000000)
+      3.56±0.1ms      4.92±0.08ms     1.38  experimental.ugrid.MeshCoordLazy.time_points(6)
+      44.1±0.5ms         55.3±1ms     1.26  experimental.ugrid.MeshLazy.time_eq(6)
+        39.3±1ms         64.9±2ms     1.65  load.LoadAndRealise.time_load((1280, 960, 5), False, 'NetCDF')
+      39.1±0.9ms       52.2±0.6ms     1.33  load.LoadAndRealise.time_load((1280, 960, 5), True, 'NetCDF')
+        35.7±2ms         49.7±1ms     1.39  load.LoadAndRealise.time_load((2, 2, 1000), False, 'NetCDF')
+        36.9±1ms         50.7±1ms     1.38  load.LoadAndRealise.time_load((2, 2, 1000), True, 'NetCDF')
+      36.8±0.6ms         50.3±1ms     1.37  load.LoadAndRealise.time_load((2, 2, 2), False, 'NetCDF')
+      37.0±0.9ms       49.7±0.9ms     1.34  load.LoadAndRealise.time_load((2, 2, 2), True, 'NetCDF')
+     3.58±0.04ms       6.09±0.2ms     1.70  load.LoadAndRealise.time_realise((2, 2, 1000), False, 'NetCDF')
+     3.68±0.06ms       6.25±0.2ms     1.70  load.LoadAndRealise.time_realise((2, 2, 1000), True, 'NetCDF')
+     3.53±0.08ms       6.05±0.2ms     1.72  load.LoadAndRealise.time_realise((2, 2, 2), False, 'NetCDF')
+     3.61±0.03ms      6.12±0.09ms     1.70  load.LoadAndRealise.time_realise((2, 2, 2), True, 'NetCDF')
+      34.7±0.7ms       42.1±0.8ms     1.22  load.TimeConstraint.time_time_constraint(3, 'NetCDF')
+      18.1±0.7ms       23.0±0.8ms     1.27  load.ugrid.BasicLoading.time_load_mesh(200000)
+      39.0±0.7ms       47.5±0.6ms     1.22  load.ugrid.BasicLoadingTime.time_load_file(200000)
+      15.3±0.4ms       22.0±0.4ms     1.44  load.ugrid.BasicLoadingTime.time_load_mesh(200000)
+      4.46±0.2ms       6.16±0.2ms     1.38  load.ugrid.DataRealisation.time_realise_data(1)
+      7.18±0.3ms       9.24±0.3ms     1.29  load.ugrid.DataRealisation.time_realise_data(200000)
+      4.50±0.3ms       6.04±0.2ms     1.34  load.ugrid.DataRealisationTime.time_realise_data(1)
+      66.1±0.8ms       86.1±0.7ms     1.30  save.NetcdfSave.time_netcdf_save_cube(1, True)
+      49.2±0.3ms         69.6±1ms     1.41  save.NetcdfSave.time_netcdf_save_mesh(1, True)

Generated by GHA run 4287641110

[trexfeathers]

The experimental.ugrid benchmarks have lazy and non-lazy equivalents. So many regressions in the lazy ones, with only one in the non-lazy ones (Mesh.time_eq), suggests this is probably related to dask-core-2023.2.1 (previously 2023.2.0).

It could possibly be libnetcdf-4.9.1 (previously 4.8.1), if there's something specific about Iris' lazy access to NetCDF. Could even be an interaction between dask-core and libnetcdf.

Either way some of these are pretty significant changes, and probably not ones we have control over - we can't pin forever. Perhaps the best we can do is warn users in our current What's New page. What does everyone think?

[pp-mo]

some of these are pretty significant changes
I totally agree. This don't look trivial to me, as they include significant %ge increases on several of the larger loading benchmarks.

We should at least check whether this is dask or netcdf ?

[pp-mo]

So many regressions in the lazy ones

Not sure I agree, we have all the load.LoadAndRealise.time_load(xxx) as well as all the load.LoadAndRealise.time_realise(xxx).
Which I think indicates that it is the basic file access for scanning + identifying structure, and not just the variable data access.

If so, would seem to point at netcdf rather than dask ?

[trexfeathers]

Step 1: I can replicate this locally ✔

[trexfeathers]

Step 2: pinning libnetcdf <=4.8.1 removes the regressions, as @pp-mo suspected.

[trexfeathers]

Step 3 (still to do): compare with Xarray to see if they have also experienced regressions (is the problem with us, or with libnetcdf?)

[trexfeathers]

Poll:

• Iris 3.5 libnetcdf pin? #5213