A small improvement to the parallel_for when task count > thread count #1839
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yufenglee
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Sep 16, 2019
Closed
This was referenced Sep 24, 2019
snnn
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Mar 12, 2020
1. Do not reuse the main thread. 2. Do not plus one when mlas calculate the number of tasks to schedule. (It was me put the plus one there) This is the second try of #1839 It's known that this change has negative performance impact on some of the models.
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Description:
A small improvement to the parallel_for when task count > thread count
Before this change: The recommended thread pool size is number of cpu cores minus one.
After this change: The recommended thread pool size is number of cpu cores
The new code is more like the parallelFor in Eigen::ThreadPoolDevice. Especially the " if (total > NumThreads()) " logic is the same.
Motivation and Context
If you have 4 cores, and 4 tasks, that's fine.
But if you have 4 cores, but 8 tasks, if one task need 1 unit time, the old code need 3 unit time, but the new code only need 2.
Related PR:
#947
#1646