Speed up idp correction function

[bennibolm]

This PR speeds up the implementation of perform_idp_correction! by

• looping over subcell interfaces for i in 2:nnodes(dg) instead of nodes for i in eachnode(dg) since no ifs are needed anymore.
• using multiply_add_to_node_vars!

Performance difference for polynomial degree of 3 (I'm using 1024 elements):

julia> @btime Trixi.perform_idp_correction!($u, $dt, $mesh, $equations, $solver, $cache)
  173.679 μs (0 allocations: 0 bytes)

julia> @btime Trixi.perform_idp_correction_new!($u, $dt, $mesh, $equations, $solver, $cache)
  137.115 μs (0 allocations: 0 bytes)

Polynomial degree of 5:

julia> @btime Trixi.perform_idp_correction!($u, $dt, $mesh, $equations, $solver, $cache)
  466.543 μs (0 allocations: 0 bytes)

julia> @btime Trixi.perform_idp_correction_new!($u, $dt, $mesh, $equations, $solver, $cache)
  308.394 μs (0 allocations: 0 bytes)

This was with Julia 1.12 on 1 thread.

[github-actions]

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Created with ❤️ by the Trixi.jl community.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.01%. Comparing base (47f4db3) to head (7fb53ab).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2644   +/-   ##
=======================================
  Coverage   97.01%   97.01%           
=======================================
  Files         561      561           
  Lines       44114    44117    +3     
=======================================
+ Hits        42796    42799    +3     
  Misses       1318     1318           

Flag	Coverage Δ
unittests	97.01% <100.00%> (+<0.01%)	⬆️

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[DanielDoehring]

Cool!

Some minor comments regarding code explanatory

[bennibolm]

The failing downstream test is expected since the test results from the sedov blast example slightly changed. I will adapt the file in Trixi2Vtk.jl when this one here is merged.

[bennibolm]

Since the first 3d PR is merged, I will also add the updated version of the 3d correction stage in this PR.

[bennibolm]

I added the new (updated) version of the 3d correction stage in e407366.
We get a similar speed up:
Polynomial degree of 3 (512 elements):

julia> @btime Trixi.perform_idp_correction!($u, $dt, $mesh, $equations, $solver, $cache)
  824.662 μs (0 allocations: 0 bytes)
julia> @btime Trixi.perform_idp_correction_new!($u, $dt, $mesh, $equations, $solver, $cache)
  740.468 μs (0 allocations: 0 bytes)

and with polynomial degree of 5:

julia> @btime Trixi.perform_idp_correction!($u, $dt, $mesh, $equations, $solver, $cache)
  3.046 ms (0 allocations: 0 bytes)
julia> @btime Trixi.perform_idp_correction_new!($u, $dt, $mesh, $equations, $solver, $cache)
  2.499 ms (0 allocations: 0 bytes)

[bennibolm]

The PR is ready to merge. Since the order of operations changed, I had to adapt some tests, including the one which is used in tests in Trixi2Vtk.jl (test files in Trixi2Vtk_reference_files). Therefore, we need to force push a PR at some point.
I suggest to first merge this PR. Then, update the reference file.
I'm no expert with down/upstream tests. Will this work then, or do we need a new release somewhere?

[bennibolm]

As discussed in the Trixi meeting before Christmas, I created trixi-framework/Trixi2Vtk_reference_files#12 in Trixi2Vtk_reference_file to update the reference files accordingly to those changes here. In my opinion, this is ready to go. @ranocha @sloede What do you say?

[ranocha]

I'll close and re-open this PR to start a new CI run.

[bennibolm]

Thanks a lot @ranocha !