Comments on: Trying to Unconfound Lisp Speeds

By: pat

pat — Tue, 30 Jun 2009 18:24:06 +0000

Indeed, that is a great deal faster, and without allocating. Thank you. I think I will write the numbers up in a separate article. But, reworking it with (incf …) instead (and I used a local variable to avoid doing (aref ret jj) multiple times) resulted in 0.40 seconds for SBCL and 0.72 seconds for Allegro.

By: Jason Cornez

Jason Cornez — Tue, 30 Jun 2009 14:11:02 +0000

In Allegro 8.1, try the following formulation instead. It avoids the boxing and results in no extra memory allocation. Hence it is quite a bit faster. Unless I’ve made a silly mistake, it should compute the same result…

-Jason

(defun mvl*-acl (matrix vec ret)
  (declare (type (simple-array single-float (12)) matrix)
           (type (simple-array single-float (3)) vec)
           (type (simple-array single-float (3)) ret)
           (optimize (speed 3) (safety 0)))
  (loop for jj fixnum from 0 below 3
     do (let ((offset (* jj 4)))
          (declare (type fixnum offset))
          (setf (aref ret jj) (aref matrix (+ offset 3)))
          (loop for ii fixnum from 0 below 3
              for kk fixnum from offset below (+ offset 3)
              do (incf (aref ret jj) (* (aref vec ii)
                                        (aref matrix kk))))))
  ret)

By: pat

pat — Sun, 28 Jun 2009 17:16:12 +0000

It does seem likely that it is boxing and unboxing floats that is causing the allocations. I would have hoped some of that could be done on the stack instead of in the heap, but….

If I get some time in the near future, I may explore the respective documentation to see how one is “supposed to” do such things with minimal memory thrashing.

Thanks….

By: Nathan

Nathan — Sat, 27 Jun 2009 18:24:59 +0000

The consing likely comes from allocating boxed single floats in the generic AREF routines and/or the arithmetic routines. SBCL and CMUCL know how to inline AREF on single-float arrays and the arithmetic routines so they don’t have to cons. Allegro and Lispworks should be able to do that too; Lispworks might require (FLOAT 0) or similar. I should think Clozure CL can do that too, although the 32-bit version obviously doesn’t. I do know that Clozure has different boxed representations for single-floats in 32-bit vs. 64-bit (the 64-bit boxed representation doesn’t require allocating any extra memory), so maybe it’s not inlining, but just relying on the generic version, which happens to not cons on 64-bit implementations.