Intel Threading Building Blocks (TBB)

Transcription

1 Intel Threading Building Blocks (TBB) SDSC Summer Institute 2012 Pietro Cicotti Computational Scientist Gordon Applications Team Performance Modeling and Characterization Lab

2 Parallelism and Decomposition TBB vs. Pthreads TBB vs. OpenMP Data parallelism,task parallelism Mixed solutions Pipelining TBB Algorithms, splittable ranges, containers Graph execution model Low level constructs

3 Algorithms parallel_for parallel_reduce parallel_scan parallel_do parallel_for_each pipeline parallel_pipeline parallel_sort parallel_invoke Generic Algorithms

4 parallel_for Parallel loop with no loop carried dependencies for ( size_t i=0; i<n; ++i) func(a[i]); class use_func{ data* a; operator()(range) { for i in range func(a[i]); parallel_for(range(0,n),use_func(a));

5 Splittable ranges Range Half open set [b,e) blocked_range<t> Partitioning split constructor divisibility partitioner class use_func{ data* a; operator()(blocked_range<int> r) { for(i=r.begin(), i!=r.end(); ++I) func(a[i]); parallel_for(blocked_range(0,n,b),use_func(a) );

6 Partitioners Recursive splitting simple_partitioner Always split auto_partitioner Load balance affinity_partitioner Try to preserve mapping data->threads parallel_for(blocked_range(0,n),use_func(a), auto_partitioner());

7 More parallel_for parallel_for<range,func>(range, Func f) parallel_for<idx,func>(idx b, Idx e, Func f) parallel_for<idx,func>(idx b, Idx e, Idx s, Func f) Partitioner Task group

8 parallel_reduce Reduce operations + operator reduce a[0:n-1] n 1 a[i] i=0 class use_func{ data* a; tmp s; operator()(range) { for i in range s+=a[i]; for ( size_t i=0; i<n; ++i) s+=a[i]; join(use_func f) { s+=f.s; use_func f(a); parallel_reduce(range(0,n),f); // result in f.s

9 Split and join Split Divide range for localized reductions Join Combine partial results A 10 A A B C B D 23

10 More parallel_reduce parallel_reduce(range r, Value 0, Func f, Red r) Replaces initial tmp values with 0 Replaces += with operator function f as op= over a range Replaces join using operator function r Partitioners Groups class r { t operator()(t lo, t ro) { return lo+ro; parallel_reduce(range(0,n),0,f(a),r);

11 parallel_scan Parallel prefix operation E.g. y[i]= i x[j] j=0 y[i] depends on y[i-1] y[0]=x[0] y[i]=y[i-1]+x[i] Parallelization Phase 1: compute partial results Phase 2: compute final prefix

12 parallel_scan phases Use tagging type parameter in operators class use_func{ data* x; data* y; data tmp; y[0]=x[0]; for ( size_t i=1; i<n; ++i) y[i] = y[i-1]+x[i]; operator(range r, pre_scan) { for(i=r.begin()+1; i!=r.end(); ++i) tmp+=x[i]; operator(range r, final_scan) { y[r.begin()] = tmp; for(i=r.begin()+1; i!=r.end(); ++i) y[i]+=y[i-1]+x[i]; parallel_scan(range(0,n),use_func(x,y));

13 parallel_scan example Split Divide range and do pre_scan reverse_join Combine partial results final_scan A A A B C B D

14 parallel_do parallel_do(iterator first, Iterator last, Func f) Apply f to iterator f can extend the range parallel_do_feeder::add class use_func{ operator()(data item, parallel_do_feeder pdf) { if(process(item)) pdf.add(new item);

15 Other parallel_* parallel_for_each Like parallel_do, but without feeder parallel_invoke Invoke up to 10 functions parallel_invoke(f0, f1,.. f9); parallel_sort(iterator begin, Iterator end) parallel_sort(iterator begin, Iterator end, Comp c) RandomAccessIterators

16 pipeline pipeline class Concatenated filters add_filter() run(live tokens) Filter class Phase of the pipeline Parallel, serial in and out of order parallel_pipeline class Same functionality, different interface

17 Pipeline example Word dictionary pipeline Read word filter Lower case filter Dictionary update filter class read_f: public filter { operator()(void* ) { b=buffers[next]; next=(next+1)%buffers_count; read(file, b); return b; class lower_f: public filter { operator()(void* b) { tolower(b); return b; class dictionary_f: public filter { operator()(void* b) { dictionary.add(b); return NULL;

18 Concurrent containers Generic containers Maps, sets, queues, vectors Concurrent operations (some) Transparent locking Next concurrent_queue concurrent_vector concurrent_hash_map Others concurrent_unordered_map/set concurrent_bounded/priority_map

19 Concurrent operations push pop_if_present pop size() Signed size type concurrent_queue

20 concurrent_vector Concurrent operations grow_by grow_to_at_least push_back operator[] Range container Has range type member Can be used in conjunction with parallel_for, reduce, scan

21 concurrent_hash_map Concurrent operations find insert erase hashing Hash function defined on keys Equality operator defined on keys Range container Has range type member Can be used in conjunction with parallel_for, reduce, scan

22 Getting started task_scheduler_init Constructor initializes the library Library activated by creating a scheduler object Number of threads is optionally specified Activation can be deferred Termination is automatic when scheduler objects are destructed Can be invoked explicitly Compiling on Gordon /opt/intel/composer_xe_2011_sp /tbb -ltbb

23 Examples /oasis/scratch/pcicotti/temp_project/tbb_si.tgz Extract a copy to a work directory Read examples code Compile and run (Interactive job!) Modify, rerun, experiment number of threads, granularity of ranges, partitioners More examples /opt/intel/composer_xe_2011_sp /tbb/examples

24 Task graph execution model Graph Nodes Functions Data/Communication managers Edges Connectors Dependencies Messages continue_message Data Support construction of DAGs of tasks

25 Thread local storage combinable enumerable Allocators scalable_allocator aligned_allocator cache_aligned_allocator zero_allocator Memory allocation

26 Synchronization Mutex (OS) mutex class recursive_mutex spin_mutex queuing_mutex spin_rw_mutex queuing_rw_mutex Atomic operations fetch_and_store fetch_and_add compare_and_swap Derived operations +=,++

27 Scheduler Task groups Group of tasks executing concurrently Tasks API Create and spawn tasks Define dependencies Wait for tasks Destroy and recycle tasks Set priorities Affinity Native threads API

28 References n.php Installing TBB Download library package Build library and examples Makefile+gnu compilers