Re: assert () taking long time

[Daniel Kraft]

Hi,

On 2013-09-19 22:06, Rik wrote:
> Are you working from the development version of Octave in the Mercurial
> repository?  The assert function has been massively re-written on the
> development branch and it may, or may not, still have performance
> issues.  Assuming you are using the latest assert.m, what kind of
> performance hit are you seeing?  Is it 1% or 10% of your script running
> time?

I didn't, but I now updated to the current hg head (as of this morning)
and the behaviour is the same.  If I enable all assert() calls (which I
already manually disabled in the places where most of the time was
spent) and do some typical calculation with my code, it takes nearly 50%
of the time (assert and deblank combined):

octave:2> profshow(profile('info'))
   #         Function Attr     Time (s)        Calls
----------------------------------------------------
 123           assert            46.269       510057
 125          deblank            25.949       510066
 211 findMeshVertices            18.137            3
 171    buildMatrices             5.205            5
 310         __line__             4.338         1690
 312      __go_line__             3.865         1690
  15           nargin             2.531      2138678
  75             find             1.990       539172
  12              max             1.960       522487
  16        binary ==             1.857      2466308

tic/toc reports 155 seconds for the whole execution.  The asserts in
question are within loops but only on simple conditions (which may
involve things like length() or indexing a vector, but not comparisons
of huge matrices or so).

> For the version in the repository, the calls to deblank could easily be
> avoided.  We pre-calculate an error message using deblank, but only
> print it if there is a problem.  You could move the calculation of the
> message inside the error checking code so that it is only generated if
> needed.  Look for the variable "in" in the code; It is used in two if
> branches so you would need to duplicate it for each if body, but that is
> simple.

I think it should be even acceptable to replace the custom error message
by something like "assertion failed" without details if the user
explicitely specifies this via a configuration option for production
runs, no?

Here are two more tests:  When I add a custom assert.m which is just an
empty function, I get a total time of 56 seconds and

   #                              Function Attr     Time (s)
------------------------------------------------------------
 205                      findMeshVertices            14.553
 166                         buildMatrices             5.239
 306                              __line__             4.335
 308                           __go_line__             3.844
 223                               cellfun             1.791
 125                              bdrygeom             1.448
 182                                ls2sd2             1.229

Even if assert is implemented like this:

function assert(cond)
  if (~cond)
    error ("assertion failed");
  endif
endfunction

which has all the "base" functionality (at least the one I need/use),
then the time is still only 57 seconds with

   #                              Function Attr     Time (s)
------------------------------------------------------------
 205                      findMeshVertices            14.509
 166                         buildMatrices             5.222
 306                              __line__             4.304
 308                           __go_line__             3.714
 223                               cellfun             1.782
 125                              bdrygeom             1.466
 182                                ls2sd2             1.257
 184                        ls2sd2>dKKTsys             1.086

So what about simply adding an option that reduces assert() to basically
this implementation in case we just have a single argument?  For my
situation, this would already improve it to the point that I wouldn't
any longer need to disable asserts manually.  Of course it is trivial to
replace assert as I just did, but it would be great if this was possible
also with Octave's built-in version.

Yours,
Daniel

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