Hello,
I met same problem too. I tested and confirmed that both Java and C++
back-end have this problem.
Test is very easy. Just reads a large file (for me, 80M) and throws the
data away. Uses -INIT_THREADS/$X10_NTHREADS to control how many threads
should be active.
Another thing I notice is that more threads you used, more times
consumed by GC. Even though you do not allocate any objects with these
threads.
However, the I/O problem seems less related to GC. This problem confused
me over 2 months. :(
Thanks
-Tetsu
On Thu, Jan 13, 2011 at 7:25 PM, Sascha Roloff <sascha.rol...@googlemail.com
> wrote:
> Dear list,
>
> I'm writing an X10 application which is suitable to parallelise. I work on
> an Intel Quad Core CPU and want to use 4 Threads. I changed X10_NTHREADS
> accordingly. The results are ok, I got almost a linear speedup at the
> calculations. But there is one problem. I also have to read a big imagefile
> at the beginning and this takes a lot more time, when I use more Threads.
>
> $ x10c++ -STATIC_CALLS -O -NO_CHECKS -o x10app Code.x10
>
> $ export X10_NTHREADS=1
> $ ./x10app
> read image data: 2336 ms
> calculation: 8290 ms
>
> $ export X10_NTHREADS=4
> $ ./x10app
> read image data: 6129 ms
> calculation: 2330 ms
>
> Here is a code snippet of reading the image:
>
> comp1 = new Array[Int]((0..(height-1))*(0..(width-1)));
> comp2 = new Array[Int]((0..(height-1))*(0..(width-1)));
> comp3 = new Array[Int]((0..(height-1))*(0..(width-1)));
>
> for([i,j] in comp1) {
> comp1(i,j) = filereader.readByte() & 0xFF;
> comp2(i,j) = filereader.readByte() & 0xFF;
> comp3(i,j) = filereader.readByte() & 0xFF;
> }
>
> I don't understand, maybe someone can help me?
>
> Sascha
>
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