[Octave-bug-tracker] [bug #54005] kron performance affected by octave_quit() calls

[A.R. Burgers]

URL:
  <http://savannah.gnu.org/bugs/?54005>

                 Summary: kron performance affected by octave_quit() calls
                 Project: GNU Octave
            Submitted by: arb
            Submitted on: Tue 29 May 2018 08:34:32 PM UTC
                Category: Interpreter
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Performance
                  Status: None
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 4.4.0
        Operating System: Any

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Details:

Kron execution times of 2 row vectors or 2 column vectors differ
significantly:


nrep = 10;
np = 10000;
tic()
ver = version
hg_id = __octave_config_info__.hg_id
for i = 1 : nrep
  a = kron(ones(np,1), ones(np, 1));
end
toc()
tic()
for i = 1 : nrep
  a = kron(ones(1, np), ones(1, np));
end
toc()


The timings are 


Elapsed time is 2.40767 seconds. (for the column vectors)
Elapsed time is 5.19106 seconds. (for the row vectors)


Moving the octave_quit() from the innermost loop to outside


diff -r cdaa884568b1 libinterp/corefcn/kron.cc                               

--- a/libinterp/corefcn/kron.cc Thu May 24 19:20:35 2018 -0700               

+++ b/libinterp/corefcn/kron.cc Tue May 29 22:26:22 2018 +0200               

@@ -63,11 +63,11 @@                                                          

   MArray<T> c (dim_vector (nra*nrb, nca*ncb));                              

   T *cv = c.fortran_vec ();                                                 

                                                                             

+  octave_quit ();                                                           

   for (octave_idx_type ja = 0; ja < nca; ja++)                              

     for (octave_idx_type jb = 0; jb < ncb; jb++)                            

       for (octave_idx_type ia = 0; ia < nra; ia++)                          

         {                                                                   

-          octave_quit ();                                                   

           mx_inline_mul (nrb, cv, a(ia, ja), b.data () + nrb*jb);           

           cv += nrb;                                                        

         } 


makes the row vector case quite a bit faster:


Elapsed time is 2.31054 seconds. (column vectors)
Elapsed time is 3.54135 seconds. (row vectors)






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