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• san_isn March 10, 2011 11:46 AM PST    Regarding scalability with number of threads of a simple CnC program Hi,   I wrote a simple program that simple generates tags and processes them (attached below). However its performance degrades when I increase the number of threads. Would very appreciate any insight has to how/why to address the scalability issue. Thanks Sandeep //Stack.cnc  <int l1stack>; <int l2stack>; <l1stack> ::  (l1compute); <l2stack> ::  (l2compute); env-><l1stack>; (l1compute)-><l2stack>; <int l1stack>;<int l2stack>; <l1stack> ::  (l1compute);<l2stack> ::  (l2compute); env-><l1stack>;(l1compute)-><l2stack>; //Stack.cpp #include <stdlib.h> #include <time.h> #include "stack.h" #include <iostream> stack_context c; int ctr = 0; // Create an instance of the context class which defines the graph int main(int argc, char** argv) {      clock_t start, end;   double elapsed;   start = clock();   for(int j = 0; j < 4; ++j)     {   for(int i = 0; i < 3000000; ++i)     {       c.l1stack.put(j*3000000+ i);     }     }      elapsed = ((double) (end-start))/CLOCKS_PER_SEC;   c.wait();   end = clock();   elapsed = ((double) (end-start))/CLOCKS_PER_SEC;   std::cout<<"Elapsed "<<elapsed<<std::endl; } int l1compute::execute(const int & t, stack_context & c ) const {   c.l2stack.put(t);   return CnC::CNC_Success; } int l2compute::execute(const int & t, stack_context & c ) const {   return CnC::CNC_Success; } Frank Schlimbach (Intel) March 10, 2011 11:05 PM PST Rate   #1 Regarding scalability with number of threads of a simple CnC program Hi Sandeep, not sure why performance goes down, but if the steps are doing nothing, then the scalability bottleneck is obvioulsy the conccurrent use of the tag-collection. How many threads are you using? There is one feature in the API (but not in the spec syntax (yet)) to reduce the overhead of CnC. We call it tag-ranges (even though the better term would be tag-sets). It is similar in spirit to TBB's ranges. Instead of putting individual tags, the API also accepts putting a bunch of tags at once and takes care for partitioning the tag-space internally. In your example, you could the following: 1. When declarting the tag_collection: typedef tbb:blocked_range< int > int_range; CnC::tag_collection< int, int_range > l1stack; In the env-code, relace your nested loop with for(int j = 0; j < 4; ++j) {     c.l1stack.put_range( int_range( j*3000000, j*3000000+3000000 ) ); } or, even better, with just c.l1stack.put_range( int_range( 0, 5*3000000 ) ); This will reduce the pressure on l1stack, but not from l2stack. A little more advance version of tag-ranges would be used to also reduce the overhead on l2stack. But first please let us know if the above would be a feasable approach in general.   san_isn March 11, 2011 2:46 PM PST Rate   #2 Reply To #1 Regarding scalability with number of threads of a simple CnC program Hi Frank,  Thanks for taking a look.  Unfortunately loading tags in bulk wouldn't be an option. I thought may be code generation is too fast to keep up with the synchronization.  Therefore I changed the code to read tags randomly from a vector (add memory latency).  Unfortunately this didn't help me either.  I have now tried on two different cpus. I guess I would wait newer hardware from intel for this code to work. -Sandeep

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