Tests fail on 12-thread Ryzen 5

[mgorny]

First noticed on 2.10.0, reproduced with cb7aed5.

$ python -c 'import numexpr; numexpr.test()'
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
Numexpr version:   2.10.1.dev0
NumPy version:     1.26.4
Python version:    3.11.8 (main, Feb 11 2024, 17:30:38) [GCC 13.2.1 20240113]
Platform:          linux-x86_64-#1 SMP PREEMPT_DYNAMIC Wed Apr  3 15:46:55 -00 2024
CPU vendor:        
CPU model:         
CPU clock speed:    MHz
VML available?     False
Number of threads used by default: 8 (out of 12 detected cores)
Maximum number of threads: 64
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======================================================================
FAIL: test_numexpr_max_threads_empty_string (numexpr.tests.test_numexpr.test_threading_config.test_numexpr_max_threads_empty_string)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/tmp/numexpr/.venv/lib/python3.11/site-packages/numexpr/tests/test_numexpr.py", line 1174, in test_numexpr_max_threads_empty_string
    self.assertEqual(detect_number_of_cores(), numexpr._init_num_threads())
AssertionError: 12 != 8

======================================================================
FAIL: test_omp_num_threads_empty_string (numexpr.tests.test_numexpr.test_threading_config.test_omp_num_threads_empty_string)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/tmp/numexpr/.venv/lib/python3.11/site-packages/numexpr/tests/test_numexpr.py", line 1167, in test_omp_num_threads_empty_string
    self.assertEqual(detect_number_of_cores(), numexpr._init_num_threads())
AssertionError: 12 != 8

----------------------------------------------------------------------
Ran 5538 tests in 3.164s

FAILED (failures=2)

[FrancescAlted]

Strange. 2.9.x is working well in that box?

[mgorny]

Yes.

$ pip install numexpr==2.9.0
Collecting numexpr==2.9.0
  Downloading numexpr-2.9.0-cp311-cp311-manylinux_2_17_x86_64.manylinux2014_x86_64.whl.metadata (7.9 kB)
Collecting numpy>=1.13.3 (from numexpr==2.9.0)
  Using cached numpy-1.26.4-cp311-cp311-manylinux_2_17_x86_64.manylinux2014_x86_64.whl.metadata (61 kB)
Downloading numexpr-2.9.0-cp311-cp311-manylinux_2_17_x86_64.manylinux2014_x86_64.whl (377 kB)
   ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 377.5/377.5 kB 1.9 MB/s eta 0:00:00
Using cached numpy-1.26.4-cp311-cp311-manylinux_2_17_x86_64.manylinux2014_x86_64.whl (18.3 MB)
Installing collected packages: numpy, numexpr
Successfully installed numexpr-2.9.0 numpy-1.26.4
$ python -c 'import numexpr; numexpr.test()'
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
Numexpr version:   2.9.0
NumPy version:     1.26.4
Python version:    3.11.8 (main, Feb 11 2024, 17:30:38) [GCC 13.2.1 20240113]
Platform:          linux-x86_64-#1 SMP PREEMPT_DYNAMIC Wed Apr  3 15:46:55 -00 2024
CPU vendor:        
CPU model:         
CPU clock speed:    MHz
VML available?     False
Number of threads used by default: 8 (out of 12 detected cores)
Maximum number of threads: 64
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----------------------------------------------------------------------
Ran 5536 tests in 4.126s

OK
$ pip install numexpr==2.10.0
Collecting numexpr==2.10.0
  Downloading numexpr-2.10.0-cp311-cp311-manylinux_2_17_x86_64.manylinux2014_x86_64.whl.metadata (7.9 kB)
Requirement already satisfied: numpy>=1.19.3 in ./venv/lib/python3.11/site-packages (from numexpr==2.10.0) (1.26.4)
Downloading numexpr-2.10.0-cp311-cp311-manylinux_2_17_x86_64.manylinux2014_x86_64.whl (378 kB)
   ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 378.3/378.3 kB 2.0 MB/s eta 0:00:00
Installing collected packages: numexpr
  Attempting uninstall: numexpr
    Found existing installation: numexpr 2.9.0
    Uninstalling numexpr-2.9.0:
      Successfully uninstalled numexpr-2.9.0
Successfully installed numexpr-2.10.0
$ python -c 'import numexpr; numexpr.test()'
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
Numexpr version:   2.10.0
NumPy version:     1.26.4
Python version:    3.11.8 (main, Feb 11 2024, 17:30:38) [GCC 13.2.1 20240113]
Platform:          linux-x86_64-#1 SMP PREEMPT_DYNAMIC Wed Apr  3 15:46:55 -00 2024
CPU vendor:        
CPU model:         
CPU clock speed:    MHz
VML available?     False
Number of threads used by default: 8 (out of 12 detected cores)
Maximum number of threads: 64
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..................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................F..F....
======================================================================
FAIL: test_numexpr_max_threads_empty_string (numexpr.tests.test_numexpr.test_threading_config.test_numexpr_max_threads_empty_string)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/tmp/venv/lib/python3.11/site-packages/numexpr/tests/test_numexpr.py", line 1174, in test_numexpr_max_threads_empty_string
    self.assertEqual(detect_number_of_cores(), numexpr._init_num_threads())
AssertionError: 12 != 8

======================================================================
FAIL: test_omp_num_threads_empty_string (numexpr.tests.test_numexpr.test_threading_config.test_omp_num_threads_empty_string)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/tmp/venv/lib/python3.11/site-packages/numexpr/tests/test_numexpr.py", line 1167, in test_omp_num_threads_empty_string
    self.assertEqual(detect_number_of_cores(), numexpr._init_num_threads())
AssertionError: 12 != 8

----------------------------------------------------------------------
Ran 5538 tests in 4.597s

FAILED (failures=2)

[FrancescAlted]

Yup. The only reason that I can see for that is PR #472, but I don't immediately see what the issue could be. Any hint @phofl?

[FrancescAlted]

Ah, I think I know what it is: https://github.com/pydata/numexpr/blob/master/numexpr/utils.py#L146-L149

        if n_cores > 8:
            # The historical 'safety' limit.
            log.info('Note: NumExpr detected %d cores but "NUMEXPR_MAX_THREADS" not set, so enforcing safe limit of 8.'%n_cores)
            n_cores = 8

The cutoff to 8 cores is because we have never experienced a speedup with more than 8 threads, and often times, slowdowns occur in these circumstances. Perhaps it is time to measure with more modern machines and decide whether to increase the threshold?

Meanwhile, the tests should be updated indeed. @phofl would you like to tackle this?

[mgorny]

Thanks!