Comments on: Functional Globals in LabVIEW 8.5 - No Loop, No Joke http://thinkinging.com/2007/09/07/functional-globals-in-labview-85-no-loop-no-joke/ an unfiltered stream of data flow consciousness Fri, 5 Sep 2008 20:16:48 +0000 http://wordpress.org/?v=2.6.1 By: Jim Kring http://thinkinging.com/2007/09/07/functional-globals-in-labview-85-no-loop-no-joke/#comment-1081 Jim Kring Wed, 19 Sep 2007 16:07:24 +0000 http://thinkinging.com/2007/09/07/functional-globals-in-labview-85-no-loop-no-joke/#comment-1081 Hi Jeff, Thanks for the fast (and correct) response ;) I'm happy to hear that you're working on it. Is there a CAR number for this issue, so that we (the community) can more easily monitor progress? Thanks, -Jim Hi Jeff,

Thanks for the fast (and correct) response ;) I’m happy to hear that you’re working on it. Is there a CAR number for this issue, so that we (the community) can more easily monitor progress?

Thanks,

-Jim

]]> By: Jeff Washington http://thinkinging.com/2007/09/07/functional-globals-in-labview-85-no-loop-no-joke/#comment-1079 Jeff Washington Wed, 19 Sep 2007 16:02:36 +0000 http://thinkinging.com/2007/09/07/functional-globals-in-labview-85-no-loop-no-joke/#comment-1079 Hello, The new feedback node was implemented by my group in LV 8.5 (and the original feedback node was implemented by my group in LV 7.0). We've done experiments to verify the discussions here and investigated the causes. It turns out that late in 8.5 we ran into incorrect behavior under certain conditions, so an extra copy was introduced to make the feedback nodes behave correctly in every scenario. This fix resulted in a performance penalty which was not present when we did performance measurements earlier in the release process. This is unfortunate, and we are investigating addressing this for future versions of LV. Correct and fast would be better than correct and slow which is better than wrong and fast. Jeff Washington Principal Engineer LabVIEW R&D Hello,
The new feedback node was implemented by my group in LV 8.5 (and the original feedback node was implemented by my group in LV 7.0). We’ve done experiments to verify the discussions here and investigated the causes.

It turns out that late in 8.5 we ran into incorrect behavior under certain conditions, so an extra copy was introduced to make the feedback nodes behave correctly in every scenario. This fix resulted in a performance penalty which was not present when we did performance measurements earlier in the release process.

This is unfortunate, and we are investigating addressing this for future versions of LV.
Correct and fast would be better than correct and slow which is better than wrong and fast.

Jeff Washington
Principal Engineer
LabVIEW R&D

]]> By: Jim Kring http://thinkinging.com/2007/09/07/functional-globals-in-labview-85-no-loop-no-joke/#comment-1018 Jim Kring Mon, 10 Sep 2007 23:04:14 +0000 http://thinkinging.com/2007/09/07/functional-globals-in-labview-85-no-loop-no-joke/#comment-1018 Jeffrey: Thanks for the extra info. I have added this to the <a href="http://wiki.lavag.org/Functional_global_variable#Performance" rel="nofollow">"Concerns>>Performance" section of the Functional Global page on the LabVIEW Wiki</a>. If you would like to add to this, feel free. :) Jeffrey: Thanks for the extra info. I have added this to the “Concerns>>Performance” section of the Functional Global page on the LabVIEW Wiki. If you would like to add to this, feel free. :)

]]> By: Jeffrey Habets http://thinkinging.com/2007/09/07/functional-globals-in-labview-85-no-loop-no-joke/#comment-1017 Jeffrey Habets Mon, 10 Sep 2007 22:45:00 +0000 http://thinkinging.com/2007/09/07/functional-globals-in-labview-85-no-loop-no-joke/#comment-1017 Jim, yes I used the show buffer allocations tool.. The differences in speed I mentioned in my first reply where partly caused by me using the select node in the feedback-solution (as by your example here) and a case in the lv2-style global (force of habit :-)). When using the select node in both solutions the lv2-style is still 1.5 times faster. When using a case as the select-mechanism, there is no difference in speed. I'm testing this with an array of 500000 dbl's btw. Other (smaller) array size's give different results, ranging from approx. 1.5 to 3 times. Jim, yes I used the show buffer allocations tool..

The differences in speed I mentioned in my first reply where partly caused by me using the select node in the feedback-solution (as by your example here) and a case in the lv2-style global (force of habit :-)).

When using the select node in both solutions the lv2-style is still 1.5 times faster. When using a case as the select-mechanism, there is no difference in speed.

I’m testing this with an array of 500000 dbl’s btw. Other (smaller) array size’s give different results, ranging from approx. 1.5 to 3 times.

]]> By: Jim Kring http://thinkinging.com/2007/09/07/functional-globals-in-labview-85-no-loop-no-joke/#comment-1012 Jim Kring Mon, 10 Sep 2007 20:34:00 +0000 http://thinkinging.com/2007/09/07/functional-globals-in-labview-85-no-loop-no-joke/#comment-1012 Jeffrey: Regarding the memory allocation, have you looked at the VI's with the show buffer allocations tool? Jeffrey: Regarding the memory allocation, have you looked at the VI’s with the show buffer allocations tool?

]]> By: Jeffrey Habets http://thinkinging.com/2007/09/07/functional-globals-in-labview-85-no-loop-no-joke/#comment-1011 Jeffrey Habets Mon, 10 Sep 2007 20:09:32 +0000 http://thinkinging.com/2007/09/07/functional-globals-in-labview-85-no-loop-no-joke/#comment-1011 I benckmarked in 8.5 (pre 8.5 it wouldn't have been possible without a loop). I tested some more and noticed some varying results.. Working with a case for the write/read selection, I get the same performance for feedback-node and lv2-style. When I replace the case with a select-primitive (this effectively seems to introduce an extra memory allocation), the lv2-style wins. I benckmarked in 8.5 (pre 8.5 it wouldn’t have been possible without a loop).

I tested some more and noticed some varying results.. Working with a case for the write/read selection, I get the same performance for feedback-node and lv2-style. When I replace the case with a select-primitive (this effectively seems to introduce an extra memory allocation), the lv2-style wins.

]]> By: Jim Kring http://thinkinging.com/2007/09/07/functional-globals-in-labview-85-no-loop-no-joke/#comment-1010 Jim Kring Mon, 10 Sep 2007 17:10:48 +0000 http://thinkinging.com/2007/09/07/functional-globals-in-labview-85-no-loop-no-joke/#comment-1010 Matt, In <a href="http://forums.lavag.org/LV2-style-globals-Ever-wondered-whether-to-use-While-Loops-or-For-Loops-t7175.html&st=40#entry35411" rel="nofollow">this post on LAVA</a> Rolf states: "And yes Jeff [Washington] mentioned that the original Feedback node was implemented by an intern and they had thought he had chosen to implement it simply as a folded shift register but that seems to not have been the case and that is why it was much slower than a shift register. In 8.5 however Jeff claimed that the Feedback register should in all aspects we as user could possibly measure, behave exactly as a shift register." I'm not sure if Jeffrey Habets benchmark was done in LabVIEW 8.5 or not. Matt,

In this post on LAVA Rolf states:

“And yes Jeff [Washington] mentioned that the original Feedback node was implemented by an intern and they had thought he had chosen to implement it simply as a folded shift register but that seems to not have been the case and that is why it was much slower than a shift register. In 8.5 however Jeff claimed that the Feedback register should in all aspects we as user could possibly measure, behave exactly as a shift register.”

I’m not sure if Jeffrey Habets benchmark was done in LabVIEW 8.5 or not.

]]> By: Matt Holt http://thinkinging.com/2007/09/07/functional-globals-in-labview-85-no-loop-no-joke/#comment-1007 Matt Holt Mon, 10 Sep 2007 15:31:15 +0000 http://thinkinging.com/2007/09/07/functional-globals-in-labview-85-no-loop-no-joke/#comment-1007 Crossing my fingers that this is NI's typical "Make it work, then make it fast" development style in full action. Crossing my fingers that this is NI’s typical “Make it work, then make it fast” development style in full action.

]]> By: Jim Kring http://thinkinging.com/2007/09/07/functional-globals-in-labview-85-no-loop-no-joke/#comment-1004 Jim Kring Sun, 09 Sep 2007 22:19:13 +0000 http://thinkinging.com/2007/09/07/functional-globals-in-labview-85-no-loop-no-joke/#comment-1004 Jeffrey: Thanks for posting your results. It's too bad that there is such a huge difference in performance. I guess we'll have to keep using the old-style for now :) Jeffrey: Thanks for posting your results. It’s too bad that there is such a huge difference in performance. I guess we’ll have to keep using the old-style for now :)

]]> By: Jeffrey Habets http://thinkinging.com/2007/09/07/functional-globals-in-labview-85-no-loop-no-joke/#comment-1003 Jeffrey Habets Sun, 09 Sep 2007 21:43:02 +0000 http://thinkinging.com/2007/09/07/functional-globals-in-labview-85-no-loop-no-joke/#comment-1003 I did a quick benchmark and it looks like the lv2 old-style still outperforms the feedback-node solution. For writing the old-style was about 2 times faster, and for reading 3 times faster. Jeffrey I did a quick benchmark and it looks like the lv2 old-style still outperforms the feedback-node solution. For writing the old-style was about 2 times faster, and for reading 3 times faster.

Jeffrey

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