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BLI: avoid invoking tbb for small workloads 

We often call `parallel_for` in places with very variable
sized workloads. When many elements are processed,
using multi-threading is great, but when processing
few elements (possibly many times) using `parallel_for`
can result in significant overhead.

I measured that this improves performance by >20% in
the refactored realize instances code I'm working on
separately. The change might also help with debugging
sometimes, because the stack trace is smaller and contains
fewer irrevelant symbols.
This commit is contained in:
Jacques Lucke 2021-12-02 12:54:35 +01:00
parent 0f89d05848
commit e130903060
Notes: blender-bot 2023-10-04 09:42:55 +02:00 
Referenced by commit c2737913db, BLI: Avoid invoking tbb for small parallel_reduce calls
Referenced by commit e9334c5df8, Geometry Nodes: Avoid parallel_for_each with a single geometry
1 changed files with 10 additions and 5 deletions
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15
source/blender/blenlib/BLI_task.hh
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@ -67,14 +67,19 @@ void parallel_for(IndexRange range, int64_t grain_size, const Function &function
return;
}
#ifdef WITH_TBB
tbb::parallel_for(tbb::blocked_range<int64_t>(range.first(), range.one_after_last(), grain_size),
[&](const tbb::blocked_range<int64_t> &subrange) {
function(IndexRange(subrange.begin(), subrange.size()));
});
/* Invoking tbb for small workloads has a large overhead. */
if (range.size() >= grain_size) {
tbb::parallel_for(
tbb::blocked_range<int64_t>(range.first(), range.one_after_last(), grain_size),
[&](const tbb::blocked_range<int64_t> &subrange) {
function(IndexRange(subrange.begin(), subrange.size()));
});
return;
}
#else
UNUSED_VARS(grain_size);
function(range);
#endif
function(range);
}
template<typename Value, typename Function, typename Reduction>