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I have a problem with experiment on my computer. I've done 300 tests of parallel algorithm (32 threads) and seen, that runtime of about 10% tests is less than others. It looks like that: we have 100 tests with runtime of each about 100 ms, then we have 30 tests with runtime ~ 80 ms and again 170 tests with runtime ~100 ms. It happens every experiment. I used OpenMP, TBB, PTHREAD, std::Thread and it happens with every parallel technology. What's the reason of that?

CPU: Intel® Core™ i7 Kaby Lake H 2800 - 3800 MHz Cores: 4 Threads: 8

Luba Philippova
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    You're oversubscribing your system a lot there and that difference is not that large still, it could just be a little random due to other processes wanting some much needed CPU attention. – Qubit Dec 24 '18 at 17:02
  • Also TBB has recommendation about minimal size of user's lambda: it should be not less than [100,000 clocks](https://www.threadingbuildingblocks.org/docs/help/reference/algorithms/parallel_for_each_func.html) – ntfs.hard Dec 24 '18 at 18:39

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