bugGNU Octave - Bugs: bug #60251, [octave-forge] (parallel) strange...


bug #60251: [octave-forge] (parallel) strange execution times

Submitted by:  Muhali <muhali>
Submitted on:  Wed 17 Mar 2021 04:51:55 PM UTC  
Category:  Octave Forge Package Severity:  3 - Normal
Priority:  5 - Normal Item Group:  None
Status:  None Assigned to:  None
Originator Name:  Open/Closed:  Open
Release:  6.1.0 Operating System:  GNU/Linux

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Wed 17 Mar 2021 06:20:18 PM UTC, comment #1: 

Starting with 4.0.0, parallel uses freshly started Octave sessions as parallel workers. These are started by the first call to parcellfun. (More are started if 'parcellfun's first argument is larger than in any call before.) This makes the first call take longer time. 9 seconds for 'nproc' starts of 'octave-cli' seems long, though...

That the second call takes longer than in version 3.1.3 may be expected (although a comparison with different Octave compilations is only rough), since the communication between the master and slave sessions in versions starting with 4.0.0 constitutes some overhead.

Olaf Till <i7tiol>
Project Member
Wed 17 Mar 2021 04:51:55 PM UTC, original submission:  

As the code below shows, the newer parallel package (4.0.0, with octave-6) has some strange execution time behavior.

pkg load parallel

n = 3000 ;
I = num2cell(1:n) ;

tic ;
C = parcellfun(nproc, @(x) 1:n == x, I, "UniformOutput", false, "VerboseLevel", 0) ;
tic ;
C = parcellfun(nproc, @(x) 1:n == x, I, "UniformOutput", false, "VerboseLevel", 0) ;

The result is

Elapsed time is 9.65733 seconds.
Elapsed time is 0.534994 seconds.

When doing the same with the old version (3.1.3, with octave-5) one gets

Elapsed time is 0.339917 seconds.
Elapsed time is 0.325187 seconds.

Muhali <muhali>


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    Follow 2 latest changes.

    Date Changed by Updated Field Previous Value => Replaced by
    2021-03-21 rik5 Carbon-CopyRemoved 72865 => -
    2021-03-21 rik5 CategoryNone => Octave Forge Package

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