Cool Tools for SPARC Systems - overview Darryl Gove

Transcription

1 Cool Tools for SPARC Systems - overview Darryl Gove Compiler Performance Engineering

2 2 Outline Throughput Computing Porting Compiling Instrumenting Optimising Debugging Threading

3 Throughput Computing 3

4 4 Using multiple cores CMT (Chip Multi-Threading) T1000 & T2000 up to 32-threads Tool to help evaluate application suitability for T1000/T2000: Various strategies: > Multiple copies > Fork & Exec > pthreads > OpenMP (-xopenmp) > Autopar (-xautopar)

5 Scaling (using pthreads or OpenMP) Throughput - tasks/second Throughput - tasks/second Simple code, nearly linear scaling to available cores Threads used UltraSPARC-T1 (6 core, 1GHz) UltraSPARC-III (2x750MHz) 5

6 6 Traditional threading trouble spots False sharing: > Multiple threads attempting to update the same cacheline. > Can be avoided. Mutex locks: > Necessary to maintain correctness. > Cannot (always) be avoided.

7 False sharing - example volatile int * results;... void* thread_code(void* v) { int i; int results[id] = 0; int id = (int)v; Threads update different variables on the same cacheline for (i=(id)*array_length; i<(id+1)*array_length; i++) { results[id]+=array[i]; } } /*results[id]=sum; */ return 0; Two threads trying to update the same cacheline

8 False sharing performance Throughput - tasks/second Throughput - false sharing Performance reduces due to false sharing on traditional system Threads UltraSPARC-T1 (6 core, 1GHz) UltraSPARC-III (2x750MHz) 8

9 9 Mutex - all threads contending for one lock void* thread_code(void* v) { int i; int id = (int)v; for (i=(id)*array_length; i<(id+1)*array_length; i++) { pthread_mutex_lock(&results_mutex); } } results+=array[i]; pthread_mutex_unlock(&results_mutex); return 0; All loop iterations are mutexed

10 Mutex constrained scaling Throughput 2 1 Throughput with mutex limited scaling Impact of mutex lock substantially reduced on CMT system Threads UltraSPARC-T1 6 cores 1GHz V880 8 cpus 1.05GHz 10

11 11 Observations False sharing impacts scaling Using mutexes can severely limit scaling Less impact on CMT processor Can be easier to write scaling applications on a CMT processor

12 Porting 12

13 13 Voice of the developer GCC compatibility Finding bugs Improving performance Using multiple threads

14 Compiling 14

15 15 Sun Studio 11 compiler and tools Free from Solaris x64, Solaris SPARC, Linux x64

16 16 GCC for SPARC Systems GCC frontend > GCC extensions > GCC debug Sun backend > SPARC optimisations > Crossfile optimisation > Profile feedback > Sun tool integration Drop in alternative for GCC Free download:

17 Instrumenting 17

18 18 Binary Instrumentation Tool (BIT) Instruments annotated binaries and libraries Provider of: > Instruction/call count data > Code coverage Compiler flag -xbinopt=prepare More information at:

19 19 BIT coverage results bit coverage -R -d nmbasic.t.exe... BIT Code Coverage Total Functions: 179 Covered Functions: 19 Function Coverage: 10.6% Total Basic Blocks: 775 Covered Basic Blocks: 508 Basic Block Coverage: 65.5% Total Basic Block Executions: 1,296 Average Executions per Basic Block: 1.67 Total Instructions: 3,168 Covered Instructions: 1,719 Instruction Coverage: 54.3% Total Instruction Executions: 6,373 Average Executions per Instruction: 2.01 Creating experiment database test.1.er

20 BIT Uncoverage 20

21 Optimising 21

22 SPOT architecture 22

23 23 Running SPOT For process that can be run multiple times: spot <app> <params> For [non-production] running process: spot -P <pid> Compiler flags: > -g [-g0 for C++] to attribute events to source > -xbinopt=prepare (plus optimisation at least -xo1) for function/instruction count info Free add on to Sun Studio 11

24 Instruction Frequency (from BIT) Instruction frequency summary information Instruction frequency detail 24

25 25 Performance Counters Time lost due to various processor stall conditions Memory consumption & system time Graph of events over time

26 26 Profile - hardware events (-X flag) Time lost to Data Cache miss events

27 Profile - time Number of times routine was called Instructions executed in each routine Time spent in each routine 27

28 Assembly level profile Source code for loop Loop entered once, trip count = ~170M Load instruction that takes the time 28

29 29 System-wide bandwidth data (-X flag) System-wide bandwidth data collected with -X flag and root permissions.

30 System-wide trap data (-X flag) System-wide trap information collected with -X flag and root permissions 30

31 Tuning and Debugging 31

32 32 Basics of ATS Automatic reoptimization and recompilation tool Does not need source code % ats -i '-xo3' a.out % ats -i '-fast -xprofile=collect' -i '-fast -xprofile=use' a.out More information at:

33 ATS uses PEC Portable Executable Code > Sun IR is kept in binary cc -xo3 -Wd,-pec t.c a.out Usual Text and Data t1.o t2.o tn.o. Intermediate Representation For Each Module 33

34 Recompiling Binaries IR is extracted and reprocessed a.out Usual Text and Data Intermediate Representation For Each Module t1.ir t2.ir tn.ir. t1.o t2.o tn.o. a.out 34

35 Automatic Tuning with Special Metric 35

36 36 Find bug Locate problem flags and problem module % ats -i 'script:findbug -xo3 -fsimple=2 -xlinkopt' a.out

37 Find the offending option then the module(s) 37

38 Threading 38

39 39 Data Race Two different threads Access the same memory location At least one access is a write Concurrently Without holding any common exclusive locks X = = X

40 Introducing RDT An on-the-fly run-time data race detection tool. Works on multi-threaded applications: Pthread Solaris thread OpenMP Sun/Cray parallel directives Mixture of the above Support platform: Solaris SPARC/x86 Technology Preview - July

41 41 Using RDT three steps Step 1: instrument the application > -xinstrument=datarace Step 2: run the application under > # collect -r on a.out Step 3: check the experimental result > # rdt test.1.er

42 Screen shot of RDT 42

43 Concluding 43

44 44 Concluding remarks Have Cool Tools to cover development cycle: > Porting (T1000/T2000) > Compiling (GCC for SPARC Systems, Sun Studio 11) > Instrumenting (BIT) > Optimising (SPOT) > Tuning and Debugging (ATS) > Threading (RDT) Available from:

45 Cool tools for SPARC Systems - overview Darryl Gove darryl.gove@sun.com