1. Porting processes to threads with MPC instead of forking Some slides from Marc Tchiboukdjian (IPDPS’12) : Hierarchical Local Storage Exploiting Flexible User - Data Sharing Between MPI Tasks

2. What you do with fork int main() { DetectorInfo * infos = loadInfo(); XCommonData * data = loadCommonData(); for (…. < tasks ) { int pid = fork(); if (pid == 0) { //do a job by sharing infos & data, return; } else { //add child to wait list } //wait all childs }

3. What is MPC  A framework for HPC developed by CEA  Target many core supercomputers  On supercompters, memory scalability of runtime become an issue  Example : MPI using one process per core on 128 cores  Require 128 times the communication buffers and whole processes address map

4. What is MPC  It provides mostly  MPI thread based runtime  OpenMP runtime  And also  Patched GCC for some TLS extensions  User threads with pthread API  A parallel NUMA aware memory allocator (my PhD. work)

5. Why is might interest you  Thread based MPI  Provide MPI tasks on top of threads instead of processes  Mecanisms to port non threaded code to this  GCC & ICC patch for automatic privatization.  Extension of TLS (HLS : Hierarchical Local Storage)  You can manage sharing with a pragma  Can select sharing level (cache, NUMA, code….)

6. MPC threads

7. Can be used to avoid fork  Looks like you use fork to share some constant memory  Thanks to automatic privatization you can move the processes into threads  HLS permit to manage segment sharing  Also handle changing data (if same changes)

8. How to use  Compile and link with patched gcc mpc_cc {YOUR_FILE}  Run with mpcrun wrapper mpcrun –p 1 –c 8 –n 8./prgm  Use pragma to manage sharing #pragma hls node(var)  Other scopes : #pragma hls cache(var) level(3)  Update content only once per instance : #pragma hls single(var) {…}

10. More in code

13. Current status which can limit  Putting objects in TLS is a research topic (I know my old team has some efforts on this with Intel, don’t know the status)  MPC provides patch for GCC 4.8  ICC can be used for automatic privatization (-fmpc-privatize) but not HLS

14. Thanks