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Check to limit nr of threads for small problems #387

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bettinaheim merged 1 commit into from
Sep 28, 2020
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Check to limit nr of threads for small problems #387

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5 changes: 4 additions & 1 deletion src/Simulation/Native/src/external/fused.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -145,7 +145,10 @@ class Fused
if (envNT == NULL) { // If the user didn't force the number of threads, make an intelligent guess
int nMaxThrds = std::thread::hardware_concurrency(); // Logical HW threads
if (nMaxThrds > 4) nMaxThrds/= 2; // Assume we have hyperthreading (no consistent/concise way to do this)
if (wfnCapacity < 1u << 20) {
if (wfnCapacity < 1ul << 14) nMaxThrds = 1;
else if (wfnCapacity < 1ul << 16) nMaxThrds = 2;
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@rmshaffer rmshaffer Sep 28, 2020 •
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Minor note: looks like this line would actually increase nMaxThrds from 1 to 2 if running on a single-core CPU? Is that the intent?

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@dbwz8 dbwz8 Sep 29, 2020

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No, but I haven't seen a 1 CPU machine in a long time. Easy to add the check if desired.

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@rmshaffer rmshaffer Sep 29, 2020

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Up to you. As you say, this is probably a rare case in practice.

else if (wfnCapacity < 1ul << 20)
{
if (nMaxThrds > 8) nMaxThrds = 8; // Small problem, never use too many
else if (nMaxThrds > 3) nMaxThrds = 3; // Small problem on a small machine
}
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