[Openmcl-devel] Optimizing a stupid benchmark

[Jonathan Fischer]

This is a stupid thing to test, I was just curious about it, and I’m wondering what obvious thing it is I’m doing wrong to get really bad results.

For starters, a silly little function to sum up an arithmetic series:

(defun sum-test-iterative ()
  (let ((sum 0))
    (dotimes (i 2147483647)
      (setf sum (+ sum i)))
    sum))

In ClozureCL 1.11, this is horribly slow and conses like crazy:

? (time (sum-test-iterative))
(SUM-TEST-ITERATIVE)
took 62,875,836 microseconds (62.875835 seconds) to run.
      2,818,179 microseconds ( 2.818179 seconds, 4.48%) of which was spent in GC.
During that period, and with 4 available CPU cores,
     55,949,019 microseconds (55.949020 seconds) were spent in user mode
      7,153,305 microseconds ( 7.153305 seconds) were spent in system mode
 20,127,468,688 bytes of memory allocated.
 10,397 minor page faults, 8 major page faults, 0 swaps.
2305843005992468481

SBCL 1.3.17 does much better:

* (time (sum-test-iterative))

Evaluation took:
  7.741 seconds of real time
  7.677832 seconds of total run time (7.594504 user, 0.083328 system)
  99.19% CPU
  18,536,585,073 processor cycles
  0 bytes consed
  
2305843005992468481

If I sprinkle in some declarations I can get SBCL down to a bit over 3 seconds, but ClozureCL’s still pretty bad:

(defun sum-test-iterative ()
  (declare (optimize speed (safety 0)))
  (let ((sum 0))
    (declare ((signed-byte 64) sum))
    (dotimes (i 2147483647)
      (setf sum (the (signed-byte 64) (+ sum i))))
    sum))

? (time (sum-test-iterative))
(SUM-TEST-ITERATIVE)
took 48,308,393 microseconds (48.308390 seconds) to run.
      2,875,113 microseconds ( 2.875113 seconds, 5.95%) of which was spent in GC.
During that period, and with 4 available CPU cores,
     42,849,312 microseconds (42.849310 seconds) were spent in user mode
      6,040,092 microseconds ( 6.040092 seconds) were spent in system mode
 20,127,468,707 bytes of memory allocated.
 14,039 minor page faults, 1 major page faults, 0 swaps.
2305843005992468481

* (time (sum-test-iterative))

Evaluation took:
  3.267 seconds of real time
  3.248668 seconds of total run time (3.228591 user, 0.020077 system)
  99.45% CPU
  7,821,424,512 processor cycles
  0 bytes consed
  
2305843005992468481

How can I help ClozureCL out here? Both of these are running 64-bit on macOS, btw.
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