multi-threading not working with v9.3.0 upgrade

[Yilin Luo]

Hello, 

I have a code that works well with multi-threading class in v9.2.0, but once I upgrade to 9.3.0 the code runs very slow and CPU usage was only 20%. The output of MultithreadInfo::n_threads() is 8 and I could see threads opened, but the speed was about 8x times slower than my previous runs. 

Running the example in Step-9 also shows the same issue. Setting MultithreadInfo::set_thread_limit() to 1 or 8 does not change the running time at all.

I tried to revert back to v9.2.0, but the multi-threading still did not work...looks like I've messed up something irreversible. Could you help me on this? Thank you!

Best

Elyn

[Wolfgang Bangerth]

Yilin -- it's very difficult to say given that you state that (i) it used to
work with 9.2.0 and (ii) now it no longer works with 9.2.0. I don't think I
have a good idea where to start poking around, given that what you describe
suggests that the issue is not with deal.II itself, but possibly with the
compiler, the C++ support libraries, whether or not you are using the bundled
or an external installation of the TBB, etc.

If you still have the installation of 9.2.0 that worked successfully, I would
try to compare the detailed.log file in the build directory with the one you
have now.

Best
W.


--
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Wolfgang Bangerth email: bang...@colostate.edu
www: http://www.math.colostate.edu/~bangerth/