[Octave-bug-tracker] [bug #58445] significant slow down in dev version for certain cellfun invocations

[Rik]

Update of bug #58445 (project octave):

                Severity:              3 - Normal => 4 - Important          
                  Status:                    None => Confirmed              

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Follow-up Comment #1:

Confirmed.  This is yet another example of the reason why we need a set of
performance tests, as well as the tests for correct function that we already
have, so that as developers we don't accidentally introduce massive
slowdowns.

I thought at first it might be a problem with for loops, because your tic/toc
bracket included the cellfun call and the for loop.  There was also a
repeatability issue in that the test used random data so there was the
possibility that the data for one version was longer and required more
processing.  I wrote a new performance benchmark which is attached as
tst_cellfun_perf.m and shown below.


nrep = 1e3;

## Load same test variable for repeatability 
load cellfun.var;

## Call function once so all m-files necessary are parsed.
## Otherwise, first time through loop will be slower than others.
cellfun ('numel', aa);

bm1 = zeros (nrep, 1);
for j = 1 : nrep
  tic;
  cellfun ('numel', aa);
  bm1(j) = toc;
end
fprintf ('cellfun(''numel''): %g secs\n', sum (bm1));

bm2 = zeros (nrep, 1);
for j = 1 : nrep
  tic;
  cellfun(@numel, aa);
  bm2(j) = toc;
end
fprintf('cellfun(@numel):  %g secs\n', sum (bm2));


The data for the test is created just once with 


aa = num2cell (rand (1000,3), 2);
save -binary cellfun.var


which is also attached as mk_cellfun_tst_var.m.

Results are


6.0.90
------------------------------------------------------------
cellfun('numel'): 0.0420563 secs
cellfun(@numel):  17.388 secs

5.2.0
------------------------------------------------------------
cellfun('numel'): 0.019412 secs
cellfun(@numel):  0.025914 secs


The difference in performance between the two versions for @numel is 671X!



(file #49176, file #49177)
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Additional Item Attachment:

File name: tst_cellfun_perf.m             Size:0 KB
    <https://savannah.gnu.org/file/tst_cellfun_perf.m?file_id=49176>

File name: mk_cellfun_tst_var.m           Size:0 KB
    <https://savannah.gnu.org/file/mk_cellfun_tst_var.m?file_id=49177>



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