The devguide quick start for Unix says to compile with
make -j $(nproc)
but to test with 3 cores
./python -m test -j3
It is really necesary to limit the test to 3 cores or is that a documentation glitch?
The default is to run tests sequentially in one process on 1 core. -jN runs in parallel N processes (in N cores if that many are available). -j0 means # cores * 2 (if hyperthreaded) + 0 (34 on my 16 core processor). Whether all cores is OK depends on what else one is doing. Trying N = 1, 2, 3, … shows how time decreases (and possibly eventually increases) as N increases. On my old 6 core machine, I tried multiple values and determined that 6 * 2 + 2 == 14 looked about as good as anything. The +2 may depend on the fact that some tests block on i/o operations. The devguide assumes a multicore machine.
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