On Fri, May 7, 2010 at 5:33 PM, Cedric Pradalier <cedric.pradalier@mavt.ethz.ch> wrote:

Cedric Pradalier wrote:

Hi,

this discussion raised my curiosity, so I created a small test program to evaluate the advantage of using shared memory. The program is quite simple: on one end a publisher is creating an image of some size, and publishing it with a timestamp given by ros::Time::now(), on the other end, a receiver is receiving the image, and recording the difference between ros::Time::now() and the image timestamp.

I made this test for 1000 images, from 640x480x1, 640x480x3, 1500x1000x3, 3000x2000x3. The results are summarised in the attached pdf.

I also attach the test file so that someone can point out if something is wrong in my test.

The bottom line is: for big object, shared memory transfer reduces significantly the delivery delay.

I hope that helps.

I also add the variation of the reception interframe time in the plot, as delivery delay is not the only parameter affected by the type of transport.

Best

--
Dr. Cedric Pradalier
http://www.asl.ethz.ch/people/cedricp

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