课件01IntegratedHandsonArchitectureSoftwareToolsver1.32.ppt

1、Overview of Intel Core 2 Architecture and Software Development Tools,May 2008,Overview of Architecture ,Two Timings,Value of area,Thread A,Thread B,11.667,+3.765,15.432,15.432,+ 3.563,18.995,Value of area,Thread A,Thread B,11.667,+3.765,11.667,15.432,+ 3.563,15.230,Order of thread execution causes n

2、on determinant behavior in a data race,The Private Clause,Reproduces the variable for each thread Variables are un-initialized; C+ object is default constructed Any value external to the parallel region is undefined Can you spot the Race Condition? Make x int i; #pragma omp parallel for for(i=0; iN;

3、 i+) x = ai; y = bi; ci = x + y; ,private(x,y),Scheduling Clause,The schedule clause affects how loop iterations are mapped onto threads schedule(static ,chunk) Blocks of iterations of size “chunk” to threads Round robin distribution schedule(dynamic,chunk) Threads grab “chunk” iterations When done

4、with iterations, thread requests next set schedule(guided,chunk) Dynamic schedule starting with large block Size of the blocks shrink; no smaller than “chunk”,#pragma omp parallel for private (gP) schedule (static, 8) for( int i = start; i = end; i += 2 ) if ( TestForPrime(i) ) gP+; ,Lab 4 Mandelbro

5、t Scheduling,Objective: create a parallel version of mandelbrot. Analyze with VTune to look for load imbalance. Modify the code to add OpenMP clauses to diminish the load imbalance and improve performance Follow the next Mandelbrot activity called Mandelbrot Scheduling in the student lab doc,Work Qu

6、euing Intel Implementation Will be part of OpenMP 3.0 (slightly differently),Independent tasks can execute concurrently Create Queue of TasksWorks on Recursive functions Linked lists, etc.,Serial,Parallel,#pragma intel omp parallel taskq while(p != NULL) #pragma intel omp task do_work(p-data); p = p

7、-next; ,Optional Lab 5 Linked List Task Queue,while(p != NULL) do_work(p-data); p = p-next; ,Objective: Use VTune to identify where to parallelize a pointer chasing code and then modify the code to implement a task queue to parallelize the application Follow the Linked List task Queue activity calle

8、d LinkedListTaskQ in the student lab doc Note: We also have a companion lab, that uses worksharing to solve the same problem LinkedListWorkSharing We also have taskq labs on recursive functions - examples quicksort iNUM;i+) for(j=0;jNUM;j+) for(k=0;kNUM;k+) cij =cij + aik * bkj; for(i=0;iNUM;i+) for

9、(k=0;kNUM;k+) for(j=0;jNUM;j+) cij =cij + aik * bkj;,Fast Loop Index,Non unit stride skipping in memory can cause cache thrashing particularly for arrays sizes 2n,Unit Stride Memory Access (C/C+),Pan ready to fry eggs,Poor Cache Uilization - with Eggs,:,Carton represents cache line Refrigerator repr

10、esents main memory Table represents cache When table is filled up old cartons are evicted and most eggs are wasted,Request for an egg not already on table, brings a new carton of eggs from the refrigerator, but user only fries one egg from each carton. When table fills up old carton is evicted,User

11、requests one specific egg,User requests 2nd specific egg,User requests a 3rd egg Carton evicted,Previous user had usedall eggs on table,:,Good Cache Utilization - with Eggs,Carton eviction doesnt hurt us because weve already fried all the eggs in the cartons on the table just like previous user,User

12、 requests Eggs 1-8,User requests Eggs 9-16,User eventually asks for all the eggs,Request for one egg brings new carton of eggs from refrigerator User specifically requests eggs form carton already on table User fries all eggs in carton before egg from next carton is requested,Lab 7 Matrix Multiply C

13、ache Effects,Objective: Explore the impact of poor cache utilization on performance with VTune Analyzer and explore how to manipulation loops to achieve significantly better cache utilization & performance Follow the Matrix Multiply Cache Effects lab in the student lab doc. Set VTune Analyzer to col

14、lect samples on a counter called MEM_LOAD_RETIRED.L2_MISS & RESOURCE_STALLS,Optional Lab 8 False Sharing,Objective: Explore False sharing with VTune analyzer to learn what counters can be used to identify this issue. Manipulate the baseline code to remove the False Sharing issue Follow the False Sharing activity in the student lab doc. Set VTune Analyzer up to collect samples on a ratio called “Modified Data Sharing Ratio”,BACKUP,Lab 6 Essentials of Vectorization,Objective: Explore how auto vectorization can dramatica