SIMD Instructions outside and inside Oracle 12c. Laurent Léturgez 2016

Transcription

1 SIMD Instructions outside and inside Oracle 2c Laurent Léturgez 206

2 Whoami Oracle Consultant since 200 Former developer (C, Java, perl, PL/SQL) Data Management on Premise and in the Cloud Blogger since (In french and discontinued) Twitter

3 Agenda SIMD Instructions, outside Oracle 2c What is a SIMD instruction? Will my application use SIMD? Raw Performance SIMD Instructions, inside Oracle 2c How SIMD instructions are used inside Oracle 2c Tracing SIMD in Oracle 2c

4 Caveats Most of the topics are from My own researches My past life as a developer Some of the topics are about internals, so: Analysis and conclusion may be incomplete Future versions of Oracle may change the features Tests have been done with Oracle , Oracle Enterprise Linux 7. (UEKR3), VMWare Fusion 8 (And VirtualBox)

5 Before we start Some fundamentals (from Dennis Yurichev s book) CPU register : [ ]The easiest way to understand a register is to think of it as an untyped temporary variable. Imagine if you were working with high-level PL and could only use eight 32-bit (or 64-bit) variables. Yet a lot can be done using just these! Instruction : A primitive CPU command. The simplest examples include: moving data between registers, working with memory and arithmetic primitives. As a rule, each CPU has its own instruction set architecture (ISA). Assembly language : Mnemonic code and some extensions like macros which are intended to make a programmer s life easier.

6 Agenda SIMD Instructions, outside Oracle 2c What is a SIMD instruction? Will my application use SIMD? Raw Performance SIMD Instructions, inside Oracle 2c How SIMD instructions are used inside Oracle 2c Tracing SIMD in Oracle 2c

7 SIMD instructions outside Oracle 2c SIMD stands for Single Instruction Multiple Data Process multiple data In one CPU instruction Based on Specific registers Specific CPU instructions and sets of instructions Not Oracle specific CPU Architecture specific Intel IBM (Altivec) Sparc (VIS) This presentation is mainly about Intel architecture

8 SIMD instructions outside Oracle 2c What is a SIMD register? It s a CPU register Wider than traditional registers (RDI, RSI, R8, R9 etc.) 28 up to 52 bits wide Contains many data

9 SIMD instructions outside Oracle 2c Scalar operation an array of 4 integers {,2,3,4} add to each value CPU CPU CPU CPU CPU Reg Reg Reg Reg Reg 4 Reg2 Reg2 Reg2 Reg2 Reg2 Reg3 Reg3 Reg3 2 Reg3 2 / Reg3 5 RAM RAM RAM RAM RAM In In In In In Out Out Out Out 2 Out LOAD ADD SAVE 4 LOAD 4 ADD 4 SAVE

10 SIMD instructions outside Oracle 2c SIMD operation an array of 4 integers {,2,3,4} add to each value CPU CPU CPU CPU SIMD Reg SIMD Reg SIMD Reg SIMD Reg SIMD Reg2 SIMD Reg2 SIMD Reg2 SIMD Reg2 SIMD Reg3 SIMD Reg3 SIMD Reg SIMD Reg RAM RAM RAM RAM In In In In Out Out Out Out LOAD ADD SAVE

11 SIMD instructions outside Oracle 2c Instruction set MMX SSE SSE2/SSE3/SSSE3/SSE 4 AVX/AVX2 AVX3 or AVX52 Register Size 64 Bits 28 bits 28 bits 256 Bits 52 bits # Registers Register Name MM0 to MM7 XMM0 to XMM7 XMM0 to XMM5 YMM0 to YMM5 ZMM0 to ZMM3 Processors Pentium II Pentium III Pentium IV to Nehalem Sandy Bridge - Haswell Skylake (initially announced but not available yet) Other Only four 32 bits single precision floating point numbers Usage expansion (two 64 bits double precision, four 32 bits integers and up to sixteen 8 bits bytes) Three operand instructions (non destructive) : A+B=C rather than A=A+B Alignements requirements relaxed

12 SIMD instructions outside Oracle 2c Intel API (C/C++) : Intel Intrinsics Guide Sample code:

13 Agenda SIMD Instructions, outside Oracle 2c What is a SIMD instruction? Will my application use SIMD? Raw Performance SIMD Instructions, inside Oracle 2c How SIMD instructions are used inside Oracle 2c Tracing SIMD in Oracle 2c

14 Will my application use SIMD registers and instructions? It depends on : Hardware Consult processors datasheets to see which instruction set extensions are used (if many) Hypervisor Some (old) hypervisors do not support modern extensions VirtualBox versions <5.0 don t support SSE4, AVX and AVX2 Hyper-V on W2008R2-SP needs patch for specific processors to support AVX

15 Will my application use SIMD registers and instructions? It depends on the Operating System AVX (256 bits) is supported from Linux Kernel >= Redhat EL5 : Oracle EL5 w/uek : AVX needs xsave kernel parameter Solaris 0 upd 0 and Solaris Windows 2008 R2 SP

16 Will my application use SIMD registers and instructions? It depends on the compiler GCC > 4.6 for AVX support Use of specific switches (-msse2, -msse4., msse4.2, -mavx, -mavx2 ) Intel C/C++ Compiler (ICC) >. for AVX Support and > 3.0 for AVX2 support Use of specific switches (-xsse4.2, -xavx, -xcore-avx2 ) Beware of optimization switches (-O,-O2, -O3) More disassemble (if you are allowed to J ) Registers Assembler instructions

17 Agenda SIMD Instructions, outside Oracle 2c What is a SIMD instruction? Will my application use SIMD? Raw Performance SIMD Instructions, inside Oracle 2c How SIMD instructions are used inside Oracle 2c Tracing SIMD in Oracle 2c

18 Raw Performance Based on a C program Used CPU: Haswell microarchitecture (Core i7-4960hq). AVX/AVX2 enabled 3 tests : No SIMD, SSE4, AVX Input: one array containing Million values. Goal: Add to each value, each million values repeated 4k, 8k, 6k and 32k times CPU Time(s) = f(#rows) Quick and Dirty Sample code available here:

19 Raw Performance 90 RAW Performance (CPU) for SIMD Instructions 80 85, CPU Time (Sec) , ,46 25, ,5 3,73 0,35 3,3,96 6,8 3,5 7, M. ROWS 892 M. ROWS 6384 M. ROWS M. ROWS NO SIMD SSE4 (XMM Registers) AVX (YMM Registers)

20 Agenda SIMD Instructions, outside Oracle 2c What is a SIMD instruction? Will my application use SIMD? Raw Performance SIMD Instructions, inside Oracle 2c How SIMD instructions are used inside Oracle 2c Tracing SIMD in Oracle 2c

21 SIMD instructions inside Oracle 2c In Memory Data Structure In Memory Compression Unit : IMCU IMCU is the unit of column store allocation Target size is M rows (controlled by _inmemory_imcu_target_rows) One IMCU can contain more than one column Each column in one IMCU is a column unit (CU)

22 SIMD instructions inside Oracle 2c In memory column store storage indexes For each column unit, min and max values are maintained in a storage index Storage Indexes provide CU pruning IMCU Pruning Information about CU available in GV$IM_COL_CU (Undocumented. See Bug ID )

23 SIMD instructions inside Oracle 2c SIMD extensions are used with In Memory storage indexes for efficient filtering. IM Storage Indexes do IMCU pruning 2. SIMD instructions apply efficiently filter predicates Prod-id IMCU Pruning Filtering with SIMD

24 SIMD instructions inside Oracle 2c Oracle 2c uses specific libraries for SIMD (and compression) Located in $ORACLE_HOME/lib libshpksse422.so for SSE4.2 extensions Compiled with ICC v2 with specific xsse4.2 switch libshpkavx2.so for AVX extensions Compiled with ICC v2 with specific xavx switch libshpkavx22.so for AVX2 extensions Not yet implemented (8 functions implemented) No ICC avx2 switch used because ICC v2 doesn t support AVX2 Thanks Tanel Pöder for this J

25 SIMD instructions inside Oracle 2c Oracle SIMD related functions Located in kdzk kernel module (HPK) Part of Advanced Compression library (ADVCMP) Easily tracked with systemtap

26 SIMD instructions inside Oracle 2c How Oracle uses SIMD extensions? It depends on many parameters OS Level : /proc/cpuinfo AVX and AVX2 support SSE4 Support only

27 SIMD instructions inside Oracle 2c Which library am I using? pmap AVX support SSE4 support

28 SIMD instructions inside Oracle 2c Which compiler options have been used? Read comment section in ELF conf]$ readelf -p.comment $ORACLE_HOME/lib/libshpkavx2.so > egrep -i 'intel gcc' egrep 'xavx mavx [ 2c] -?comment:intel(r) C Intel(R) 64 Compiler XE for applications running on Intel(R) 64, Version 2.0 Build / -DNTEV_USE_EPOLL -DNET_USE_LDAP -xavx Read the corresponding compiler documentation

29 SIMD instructions inside Oracle 2c How are SIMD registers used by Oracle? GDB To get the call stack (backtrace) To set breakpoints on interesting functions To view register contents (traditional and SIMD) Info registers for traditional registers Info all-registers for all registers (SIMD reg included) (gdb) print $ymmx.<format> Format can be v8_float, v4_double, v32_int8, v6_int6, v8_int32, v4_int64, or v2_int28

30 SIMD instructions inside Oracle 2c In red, register content has been modified In blue, the second part of the SIMD registers (28 bits) is empty

31 SIMD instructions inside Oracle 2c Oracle IM can use AVX or SSE4 extensions for SIMD operations When AVX is used It uses only 28 bits out of 256 bits wide registers AVX adds new register-state through the 256-bit wide YMM register file Explicit operating system support is required to properly save and restore AVX's expanded registers between context switches Without this, only AVX 28-bit is supported

32 SIMD instructions inside Oracle 2c The culprit Oracle is supported from EL5 onwards EL5 Redhat Kernel is and this flag (xsave) is supported from kernels For compatibility reasons, Oracle has to compile its code on kernels

33 Agenda SIMD Instructions, outside Oracle 2c What is a SIMD instruction? Will my application use SIMD? Raw Performance SIMD Instructions, inside Oracle 2c How SIMD instructions are used inside Oracle 2c Tracing SIMD in Oracle 2c

34 Tracing SIMD in Oracle 2c Interesting components to trace for SIMD and/or IMCU Pruning are : ADVCMP_DECOMP.* ADVCMP_DECOMP_HPK : SIMD functions ADVCMP_DECOMP_PCODE : Portable Code Machine (usually not related to specific CPU instructions) IM_optimizer Gives information about CBO calculation related to IM

35 Tracing SIMD in Oracle 2c ADVCMP_DECOMP ADVCMP_DECOMP_HPK Information is available in the trace file (for each IMCU processed) Used library and function Number of rows and counting algorithm Processing rate (comparison and decompression if relevant) But nothing on the results of the processing L

36 Tracing SIMD in Oracle 2c ADVCMP_DECOMP ADVCMP_DECOMP_HPK Gives information about SIMD function usage and filtering (after IMCU pruning) Example: inmemory table with NO MEMCOMPRESS or DML compression

37 Tracing SIMD in Oracle 2c ADVCMP_DECOMP ADVCMP_DECOMP_HPK Example: inmemory compressed table SIMD are used only in the kdzk_eq_dict functions

38 Tracing SIMD in Oracle 2c My thoughts about compression/decompression NO MEMCOMPRESS / COMPRESS FOR DML kdzk*dynp* functions (ex: kdzk_eq_dynp_6bit, kdzk_le_dynp_32bit etc.) FOR QUERY LOW / QUERY HIGH Dictionary Encoding (LZW?) : kdzk_*dict* functions (ex: kdzk_eq_dict_7bit, kdzk_le_dict_4bit etc.) Run Length Encoding: kdzk_burst_rle* functions (ex: kdzk_burst_rle_8bit, kdzk_burst_rle_6bit ) Bit packing compression: kdzk*fixed* functions (ex: kdzk_ge_lt_fixed_32bit, kdzk_lt_fixed_8bit )

39 Tracing SIMD in Oracle 2c My thoughts about compression/decompression FOR CAPACITY LOW FOR QUERY LOW + additional proprietary compression (OZIP) Functions: ozip_decode_dict*, kdzk_ozip_decode* (Ex: kdzk_ozip_decode_dydi, ozip_decode_dict_9_bit etc.) FOR CAPACITY HIGH FOR QUERY HIGH + heavy weigth compression algorithm Compression/decompression method depends on: Datatype Column Compression Unit size Column contents

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