Can't get speed up !
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Hi,
I've just learned about Matlab Parallel Computing Toolbox. I'm studying about it. In the beginning and for taking motivation i tried some simple codes to get speed up. But all of my parallel results were worse than serial ones. I know about overhead of data communication between cores. So i wrote a code that have least data communication but likewise before the parallel execution time was longer than serial. I execute parallel code on two workers. My CPU is Intel Core 2 Duo 2.26 Ghz. CPU usage is 100% while running parallel code and 50% while running serial code.
I also tried a code that i found in net. The writer had claimed speed of for the code is 1.92 using 2 workers. But i got 0.96 !
I'm so disturbed!
2 Comments
Answers (2)
john
on 2 Dec 2012
2 Comments
Walter Roberson
on 2 Dec 2012
Try reversing the order of the subscripts, producing a 4 million by 2 output, so that there would not be any cache-line contention. Also, try vectorizing, e.g.,
A(j, :) = sin(j + (1:4000000));
with no "for k" loop.
john
on 2 Dec 2012
Edited: john
on 2 Dec 2012
6 Comments
Walter Roberson
on 29 Dec 2012
Those machines haven't been sold for a number of years. And MATLAB has not been supported on them for a fair number of releases.
Bradley Stiritz
on 22 Jan 2013
Regarding Walter's 12/2/2012 comment, I requested documentation reference from Mathworks support & received this reply:
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"While working with MATLAB in general and also with PCT, row-wise access in same column will be faster than column-wise access in same row. This is because, in MATLAB, matrix elements belonging to the same column are located in consecutive locations of memory, while elements belonging to the same row of the matrix are located in non-consecutive locations of memory.
The following link from the Mathworks website highlights the above mentioned fact and also provides additional information on "Speeding up MATLAB Applications"
Also, please see the following MATLAB Documentation link for additional details on profiling and improving parallel code:
Unfortunately, we cannot recommend any books. However, it would be highly recommended to go through the webinars mentioned in the link below:
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Hope this helps..
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