The Implementation of Cilk-5 Multithreaded Language

Transcription

1 The Implementation of Cilk-5 Multithreaded Language By Matteo Frigo, Charles E. Leiserson, and Keith H Randall Presented by Martin Skou 1/14

2 The authors Matteo Frigo Chief Scientist and founder of Cilk Arts Ph.D. in 1999 from the Department of Electrical Engineering and Computer Science at MIT. Awards George M. Sprowls award for outstanding doctoral dissertations in computer science at MIT Charles E. Leiserson Chairman, Chief Technology Officer and Founder of Cilk Arts Professor of Computer Science and Engineering at MIT MacVicar Faculty Fellow at MIT ACM Fellow Keith H. Randall Software engineer at Google Ph.d from MIT 2/14

3 The Paper ACM SIGPLAN Notices 1998 Association for Computing Machinery's Special Interest Group on programming languages Most Influential PLDI Paper Award 2008 A paper presented at the PLDI held 10 years prior to the award year. Includes a prize of $1,000 Programming Language Design and Implementation (PLDI) One of the ACM SIGPLAN's most important conferences. 3/14

4 Introduction to Cilk Language for multithreaded parallel programming based on C. Faithful extension of C It can on one processor scales down to run nearly as fast as the serial version of C, called C elision Designed for general-purpose parallel programming Has a scheduler that allows the performance of programs to be estimated Developed by the MIT CSAIL Supercomputing Technologies Group under the leadership of prof. Charles Leiserson. in 1994 Funding Supported in part by NSF Previous support in part by DARPA Latest version is Designed on the work-first principle Reduce the work overhead 4/14

5 Introduction to Cilk Performance of a Cilk computation work total execution time in serial critical-path length execution time on a infinite number of processors Uses a workstealing scheduler In Cilk-1: scheduler optimized only at compile time in Cilk-5: scheduler optimize both at compile time and run time 5/14

6 The Cilk language Uses keywords cilk identifies a function which is written in Cilk spawn Indicates that the procedure call it modifies can safely operate in parallel with other executing code sync Indicates that execution of the current procedure cannot proceed until all previously spawned procedures have completed and returned their results to the parent frame inlet Identifies a function defined within the procedure as an inlet abort Can only be used inside an inlet Tells the scheduler that any other procedures that have been spawned off by the parent procedure can safely be aborted 6/14

7 Example in Cilk #include tstdlib.h> #include <stdio.h> #include <cilk.h> cilk int fib (int n) { if (n(2) return n; else { int x, y; x = spawn fib (n-1); y = spawn fib (n-2); sync; return (x+y) ; } cilk int main (int argc, char *argv[]) { int n. result; n = atoi(argv[1]); result. = spawn fib(n); sync ; printf ( Result: %d\n, result) ; return 0: } cilk int fib (int n) { int x = 0; inlet void summer (int result) { x += result; return; } } if (nt2) return n; else c { summer(spawn fib (n-l)); summer(spawn fib (n-2)); sync; return (x); } 7/14

8 Cilk's compilation strategy The Cilk complier is called cilk2c Generate two clones fast little support for parallelism operates as the C elision does slow full support for parallelism, along enclosed overhead 8/14

9 Cilk's scheduling algorithm worker (processor) Maintains a ready deque A double ended queue of ready procedures Has a head and a tail Operates on its local tail end of the queue If the queue is empty (idle) it change to a thief thief Steal procedures from other workers Take form the head end of the other workers queue victim Worker losing procedures 9/14

10 Cilk's scheduling algorithm When a procedure is spawned start the as a fast clone if the procedures is getting stolen converted to a slow clone The stealing from the head, and convert to slow clone invariant that fast has not been stolen no descendants of a fast clone has been stolen 10/14

11 Stealing procedures Thief can get a procedure and change head to 3 Victim can change tail to 5 and get a procedure Victim will change tail to 4, if no thieves interfere, victim gets the procedure, if there are then If thief finds H>T, it stops trying If victim finds H>T, it restart and try again If thief try to steal, it fails if the victim try, it fails and control return to the runtime system 11/14

12 Conclusion Cilk-5 has better use of the work-first principle You can remove the Cilk keyword in C program and run it like a normal C program It uses compiled clones and queues to enhance the parallel performance 12/14

13 My comments More difficult than first expected Give a good overview over how some of the features in Cilk-5 is implemented The Cilk language seem so difficult to program i, if the user do understand C 13/14

14 Your comments Thank You 14/14