remove allocations in combine_surfaces

[juliasloan25]

Purpose

Before we were calling the allocating get_field method. Now we remap and store the surface field in a temp coupler field, so we don't allocate. To me it's also more readable now which is nice.

Content

• remove allocations in combine_surfaces by remapping the surface field of each simulation onto a temp coupler field
• update tests
• check buildkite results as compared to main
• check buildkite performance as compared to main

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• I have read and checked the items on the review checklist.

[juliasloan25]

This change actually slightly worsens performance. I think it's because of runtime dispatch on the field_name Val, so I'm restructuring this function a bit

[juliasloan25]

Ok, with the current state of this PR it does speed up simulations. For example comparing this build to main we see the following SYPD changes:

• GPU slabplanet albedo from function: 2.174 SYPD --> 3.017 SYPD
• GPU AMIP diag. EDMF + bucket: 0.15 SYPD --> 0.274 SYPD
• GPU CMIP with prescribed sea ice: 4.426 SYPD --> 5.511 SYPD

However runs with integrated land has the opposite trend:

• AMIP integrated land non-spun up IC test: 0.204 SYPD --> 0.12 SYPD
• AMIP ED only + integrated land: 0.415 SYPD --> 0.321 SYPD
• AMIP diag EDMF + integrated land: 0.149 SYPD --> 0.121 SYPD

[juliasloan25]

physical results
unchanged: slabplanet with albedo from function, CMIP with prescribed sea ice
changed (only MO length, precipitation): ED only + bucket, diag EDMF + bucket, AMIP ED only + integrated land

[juliasloan25]

I did some investigating into why this PR slightly slows down the benchmark, and it comes down to the following. When we swap the roles of remap and remap! in #1594 this should be fixed and then we can apply this PR and should see speedup.

• get_field! allocates more than get_field

julia> @allocated Interfacer.get_field!(csf.scalar_temp1, sim, Val(:area_fraction))
160

julia> @allocated Interfacer.get_field(sim, Val(:area_fraction), boundary_space)
32

this is because:

• remap! allocates more than remap

julia> @allocated Interfacer.remap!(field2, field1)
128

julia> @allocated Interfacer.remap(field1, boundary_space)
32

• using zero(field) in broadcasted ifelse allocates (we do this in many places and need to remove them all)

julia> @allocated combined_field .+=
                       area_fraction .*
                       ifelse.(area_fraction .≈ 0, zero(combined_field), surface_field)
6544

julia> @allocated combined_field .+=
                       area_fraction .*
                       ifelse.(area_fraction .≈ 0, zero(eltype(combined_field)), surface_field)
272

julia> @allocated combined_field .+=
                       area_fraction .*
                       ifelse.(area_fraction .≈ 0, 0, surface_field)
272