tinyasm: avoid copying the block dofmap in BlockJacobi::solve() - #5348
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manishpaulish wants to merge 1 commit into
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tinyasm: avoid copying the block dofmap in BlockJacobi::solve()#5348manishpaulish wants to merge 1 commit into
manishpaulish wants to merge 1 commit into
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dofsPerBlock is a vector<vector<PetscInt>>, so `auto dofmap = dofsPerBlock[p]` deduces by value and heap-allocates + copies the block's dofmap on every block, on every application of the preconditioner. solve() runs once per Krylov iteration and block counts are typically in the thousands, so this is on the order of a million small allocations per linear solve. Bind by const reference instead. No behavioural change: dofmap is only read. A standalone microbenchmark mirroring the loop structure (20k blocks, dof in [4,20], 50 applications, -O2) measures the copy at 11-13% of solve() runtime.
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dofsPerBlockis avector<vector<PetscInt>>, soauto dofmap = dofsPerBlock[p];deduces by value and heap-allocates plus copies the block's dofmap on every block, on every application of the preconditioner.
solve()runs once per Krylov iteration and block counts are typically in the thousands, so this is on the order of a million small allocations per linear solve.Binding by const reference instead. No behavioural change,
dofmapis only read.A standalone microbenchmark mirroring the loop structure (20k blocks, dof in [4, 20], 50 applications,
-O2) puts the copy at 11 to 13 percent ofsolve()runtime, consistent across runs. That is a microbenchmark rather than a real solve, so treat the exact figure as indicative, but the mechanism is straightforward enough.