Profiling & Debugging

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1 Prfiling & Debugging CISC 879 Tristan Vanderbruggen & Jhn Cavazs Dept f Cmputer & Infrmatin Sciences University f Delaware 1

2 Lecture Overview Prfiling and Debugging Why? Tls Data sets Race Cnditin and Deadlck Task graph and allcatin Examples: Race cnditin with OpenMP sectins Deadlck with OpenMP sectins and lck Crrect OpenMP prgrams Cmmunicatin Interlck with MPI 2

3 1.a - Why Prfiling? A prgram cannt be executed faster than its slwest part Large applicatins can have multiple slw parts! Bttleneck are difficult t find. Prfiling tl help t find where mst time spent 3

4 1.b - Tls Gprf ValGrind MemCheck CallGrind VTune 4

5 1.b - Gprf: Cmpile Step gprf: GNU prfiling Require specifically cmpile binary Have the prgram wrking, NOT a debugger Add the ptin -pg t gcc & linker $> gcc -pg -c target.c - target. $> link -pg target. - target_binary 5

6 1.b - Gprf: Run T get a prfile f yur applicatin Run the applicatin as usual $>./target_binary [applicatin-ptins] It generate a file gmn.ut, it is nt readable gprf create a human readable prfile $> gprf target_binary 6

7 1.b - Gprf: utput Flat prfile: Each sample cunts as 0.01 secnds. % cumulative self self ttal time secnds secnds calls ms/call ms/call index % time [1] name 0.00 fmtimes 0.09 cal_learned_func 0.00 plynmial self children called name <spntaneus> main [1] /1 getalphafrmtrainset [3] / plynmial [5] /6441 takestep [7] /6441 examineexample [2] [4] cal_learned_func [4] / plynmial [5] / fmallchandle [10]

8 1.b - ValGrind ValGrind is a classic dynamic analysis tl Memry checking with memcheck Cache analysis with cachegrind Call graph with the tl callgrind 8

9 1.b - ValGrind - MemCheck $> valgrind --tl=memcheck./app Memry errr detectr Accessing memry yu shuldn't Using undefined values Incrrect freeing f heap memry Overlapping src and dst in memcpy Memry leaks 9

10 1.b - ValGrind - MemCheck $> valgrind --tl=memcheck./app Memry errr detectr Accessing memry yu shuldn't verrunning and underrunning heap blcks verrunning the tp f the stack accessing memry after it has been freed Using undefined values Incrrect freeing f heap memry Overlapping src and dst in memcpy Memry leaks 10

11 1.b - ValGrind - MemCheck $> valgrind --tl=memcheck./app Memry errr detectr Accessing memry yu shuldn't Using undefined values values that have nt been initialised derived frm ther undefined values Incrrect freeing f heap memry Overlapping src and dst in memcpy Memry leaks 11

12 1.b - ValGrind - MemCheck $> valgrind --tl=memcheck./app Memry errr detectr Accessing memry yu shuldn't Using undefined values Incrrect freeing f heap memry duble-freeing heap blcks mismatched use f mallc/new/new[] versus free/delete/delete[] Overlapping src and dst in memcpy Memry leaks 12

13 1.b - ValGrind - MemCheck $> valgrind --tl=memcheck./app Memry errr detectr Accessing memry yu shuldn't Using undefined values Incrrect freeing f heap memry Overlapping src and dst in memcpy Memry leaks 13

14 1.b - ValGrind - CallGrind Using callgrind: Cmpile with -pg Run the applicatin with valgrind and callgrind $> valgrind --tl=callgrind binary N human readable utput KCacheGrind prvide visualizatin f the call graph 14

15 1.d - Visualizatin 15 2

16 1.d - Visualizatin Dem time! 16

17 1.c - Using ValGrind n Parallel Apps Threads safe n prblem with OpenMP fr MPI mpirun launches valgrind, nt the ppsite: mpirun [mpi-pts] valgrind [valgrind-pt]./app memcheck reprt large amunt f false errrs an MPI wrapper exist fr MemCheck Reducing the number f false psitive 17

18 Vtune surce: 18

19 Quick Overview f VTune Perfrmance Prfiles Htspt Hardware-Event Based Sampling (EBS) Lcks and waits analysis Thread Prfiling Visualize thread interactins n timeline Balance wrklads Hardware event sampling surce: Surce cde view 19

20 Example: Htspt Analysis surce: 20

21 Example: OpenMP Analysis Identifies where yur applicatin is waiting n synchrnizatin bjects r I/O peratins. Discvers hw these waits affect yur applicatin perfrmance. surce: 21

22 Example: OpenMP Analysis Output1 Mre detailed infrmatin Time infrmatin - Ttal, wait, spin, Tp waiting bjects - In this example, OMP Jin has the highest wait time surce: 22

23 Example: OpenMP Analysis Output1 Yu can see hw effectively using prcessr cres and get insights hw t change yur prgrams t run faster Each thread s run and wait Transitins between threads surce: 23

24 Example: MPI Analysis Use amplex-cl cmmand t cllect data and pst-prcess results Example Individual result directry will be created fr each spawned prcess > mpiexec -n 4 amplex-cl -r my_result htspt -- my_app [my_app ptins] -cllect This will create result directry fr 4 prcesses named my_result.1 t my_result.4 Using GUI viewer t analyze each result surce: 24

25 Example: MPI Analysis surce: 25

26 Future Wrk fr Vtune Upcming updates Will be part f Intel Cluster Studi XE Will be supprted n clusters surce: 26

27 1.d - Data Sets Withut gd data set : results are meaningless 4 criteriums: Nt t small: initializatin Nt t big: prfiling take lnger Gd cverage: irregular cde may need multiple dataset t shw all the bttleneck Generic: special cases are always dangerus 27

28 2 Cmmn Parallelism Bugs 28

29 2 - Task Decmpsitin View The fllwing task graph: initializes tw data-structures A and B then sets A using B, and B using A 29

30 2.a - OpenMP sectins 30

31 2.a - OpenMP sectins This cde culd: Write in a r b befre they are fully initialize What if sme memry have yet nt been allcated. It is a Race Cnditin 31

32 2.a - Race Cnditin 32

33 2.b - OpenMP Lcks We have t add sme synchrnisatins We will use lcks... 33

34 2.b - OpenMP lcks a lck is a synchrnizatin bject It can be set by ne thread nly becming wner f the lck Only the wner can release a lck Dn't frget t initialize and destry the lcks 34

35 2.b - OpenMP lcks API: decl: init: set: unset: destry: test: mp_lck_t lck; vid mp_init_lck(&lck); vid mp_set_lck(&lck); vid mp_unset_lck(&lck); vid mp_destry_lck(&lck); int mp_test_lck(&lck); 35

36 2.b - OpenMP lcks 36

37 2.b - Deadlck 37

38 2.c - OpenMP Race Cnditin 38

39 3 - Cmmunicatins Interlck We want t build a cmmunicatin ring with MPI n-1 39

40 3.a - Linear Chain 0 #0 Recv... 1 n-1 #1 #2 #n-1 Send Send Send Recv Recv 40

41 3.b - Ring with Interlck n-1 #0 #1 #2 #n-1 Send Send Send Send Recv Recv Recv Recv 41

42 3.c - Ring with Async Cmm n-1 #0 #1 #2 #n-1 Isend Isend Isend Isend Irecv Irecv Irecv Irecv 42

43 Links Sectin n MPI 43

Parallel Processing in NCAR Command Language for Performance Improvement

Parallel Processing in NCAR Command Language for Performance Improvement Parallel Prcessing in NCAR Cmmand Language fr Perfrmance Imprvement Ping Gu, University f Wyming Mentr: Wei Huang, NCAR C- Mentr: Dave Brwn, NCAR August 1, 2013 Intrductin and Mtivatin ² The NCAR Cmmand