I was trying to compare the performance of copying a Rail[Byte] between 2
places using Rail.async and using "at". Each place is running on a different
host, and the network speed is 1000Mb/s.
The first method:
1. A rail is created
2. A GlobalRef to that rail is created
3. Used At to move to the second place -> here I expect that "at" will need
to copy only the GlobalRef, not the whole array.
4. Used Rail.asyncCopy from the second place to copy the array using the
GlobalRef
The second method:
1. A rail is created
2. Used At to move to the second place -> here I expect that "at" will
implicitly copy the whole rail, that is why I expected it to be slower than the
"at" in the first method.
3. Used Rail.copy from the second place to copy the array
That is the used program code:
import x10.util.Timer;
public class TestRemoteCopy {
public static def main(args:Rail[String]) {
//Create Rail and Initialize it
val size = Long.parse(args(0));
val source:Rail[Byte] = new Rail[Byte](size);
val sourcePlace = Place.places()(0);
val destPlace = Place.places()(1);
for (var i:Long = 0; i < size; i++){
source(i) = (i%128) as Byte;
}
//Copy using Rail.asyncCopy
val gr = GlobalRail[Byte](source);
val timeBeforeAt = Timer.milliTime();
at (destPlace){
Console.OUT.println("At
Time["+(Timer.milliTime()-timeBeforeAt)+"] ...");
val dest:Rail[Byte] = new Rail[Byte](size);//1<
val timeBeforeAsyncCopy = Timer.milliTime();
finish Rail.asyncCopy(gr, 0, dest, 0, size);
Console.OUT.println("AsyncCopy
Time["+(Timer.milliTime()-timeBeforeAsyncCopy)+"] ...");
}
//Copy using at
val timeBeforeSecondAt = Timer.milliTime();
at(destPlace){
Console.OUT.println("Second At
Time["+(Timer.milliTime()-timeBeforeSecondAt)+"] ...");
val dest:Rail[Byte] = new Rail[Byte](size);
val timeBeforeSecondCopy = Timer.milliTime();
Rail.copy(source, 0, dest, 0, size);
Console.OUT.println("Second Copy
Time["+(Timer.milliTime()-timeBeforeSecondCopy)+"] ...");
}
}
}
These are some results, time is printed in milliseconds:
Rail Size: 1024 bytes
Native X10:
At Time[4305] ...
AsyncCopy Time[1] ...
Second At Time[4305] ...
Second Copy Time[0] ...
Managed X10:
At Time[4521] ...
AsyncCopy Time[31] ...
Second At Time[4308] ...
Second Copy Time[1] ...
Rail Size: 1048576 bytes (1024*1024)
Native X10:
At Time[4306] ...
AsyncCopy Time[10] ...
--> using "at" hangs
Managed X10:
At Time[4534] ...
AsyncCopy Time[106] ...
Second At Time[4331] ...
Second Copy Time[0] ...
I have some questions based on these numbers:
1) Why "at" in the first method, which is supposed to copy only a GlobalRef, is
taking as much time or even more time than the second method which copies the
whole rail?
2) Is there a maximum limit on the data size that "at" can copy in native X10?
3) The above numbers suggests that using "at" for copying rails is more
preferable than using Rail.asyncCopy. Is this conclusion correct?
?Best Regards,
Sara
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