Go to Post .. if everybody else is buying all the thingamabobs so they can practice shoving balls into the whatsit. Maybe what you really want is to buy thingys so you can build a practice whojidingle. Being the only whojidingle robot can be a real advantage come alliance picking time ... - ChrisH [more]
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Unread 04-08-2015, 23:03
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Re: Elevator Motion Profiling / PID Ramping

Quote:
Originally Posted by MrRoboSteve View Post
The JVM has changed a lot since the 1.3 version that was used on the cRIO.

Do we know what the startup command line looks like for the Java VM? I am curious to see if there are special settings regarding garbage collection.

You want to do GC tuning using the command line parameters, not by calling System.GC(). System.GC() can be undesirable as it can trigger a full GC when you shouldn't need one. http://stackoverflow.com/questions/6...gc-do-anything has some discussion.

This article discusses the tradeoffs in GC tuning. If I was having issues like this, I'd want to be looking at the output of -verbose:gc to see if I had big pauses. Then I'd experiment with the parallel collector, using in particular -XX:MaxGCPauseMillis to set a cap to the amount of time spent in GC. You want lots of very short GC runs in the younger generations.

I'd also set -Xmx and -Xms to the same value, large enough that -verbose:gc never shows a full GC occurring during a run. If you're getting full GC runs occurring, you probably need to look at changes in your program to reduce allocation as there's too much memory pressure.
I realize that this conversation is a bit dormant, but I do have a question about command line parameters. Can we modify the command that runs our robot code by adding parameters like the ones you mention here? I see where to do that (I don't have a roboRIO handy, but I believe that the command is stored in the file /home/lvusr/robotCommand) but want to know if it is "competition legal". I don't see any specific reason that it wouldn't be legal and I really hope that it is.
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Last edited by mmaunu : 04-08-2015 at 23:04. Reason: Edit to path
 


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