Why is there no good acceleration of parallel testing of Astropy with pytest-xdist?

Question

I run Astropy tests in parallel using the option python setup.py test --parallel Non my Macbook (4 real cores, solid state drive) that pytest-xdist uses to run ~ 8000 tests in parallel.

I tried different Nin the range from 1 to 10, but in all cases I can only get accelerations of about 2, but I expected to get acceleration in the range of 3 to 4 (since the launch of tests should be limited by the CPU).

Why is speed decreasing and how can I get good accelerations (using several cores on one computer)?

Update

I tried the ramdisk suggestion from @Iguananaut: diskutil erasevolume HFS+ 'ramdisk' hdiutil attach -nomount ram://8388608 mkdir//ramdisk/tmp python setup.py test -a '--basetemp =//ramdisk/tmp' --parallel 8 > ~ 2.2 ~ 2.0 SSD. , - 3 4. , - .

Answer 1

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