An In Depth Look at VOLK

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1 An In Depth Look at VOLK The Vector-Optimize Library of Kernels Nathan West U.S. Naval Research Laboratory 26 August 2015 (U) 26 August / 19

2 A brief look at VOLK organization VOLK is a sub-project of GNU Raio Sub-maintainer: Nathan West (that s me!) Coe c Free Software Founation license uner GPLv3 Submit issues an pull requests through (U) 26 August / 19

3 What s a VOLK? VOLK: Vector-Optimize Library of Kernels Collaboration, compatibility, an spee (in that orer) A library of functions optimize for various CPU architectures usually this means SIMD An API (an ispatcher) for calling the fastest coe for your machine A buil system for coe targetting specific instruction sets/architectures (U) 26 August / 19

4 Outline We will cover the priorities of VOLK in reverse orer: 1 Spee 2 Compatibility 3 Collaboration Goals: Become fluent in VOLK Know how to a a protokernel Know how to a a kernel Know how to make VOLK work for your project Know where to look to support new harware (U) 26 August / 19

5 Motivation: a NEON register view of 32fc 32f ot pro 32fc (U) 26 August / 19

6 Motivation: Disassemble C Complex Dot Prouct excerpt Coe can be inefficient even when harware features are use 1. l o o p 1 mov r11, r copy new a r e s s avec 3 mov r10, r copy new a r e s s bvec v l {16, 18, 20, 22 }, [ r11 ]! 5 a r9, r9, number += 1 cmp r9, number < h a l f p o i n t s? 7 a r8, r8, c a l c u l a t e n e x t avec a r e s s a r4, r4, c a l c u l a t e n e x t bvec a r e s s 9 v l {24, 26, 28, 30 }, [ r10 ]! v l {17, 19, 21, 23 }, [ r11 ] 11 v l {25, 27, 29, 31 }, [ r10 ] 13 <s n i p p e NEON ot p r o u c t ops> 15 bcc. l o o p r e p e a t h a l f p o i n t s t i m e s (U) 26 August / 19

7 Problem: Architecture-optimize coe is not portable Historical solution is #ifef fences Meta-compilers exist (ORC, Spiral, PEACHPy) This brings us to VOLK s secon concern: compatibility (U) 26 August / 19

8 Compatibility All problems in computer science can be solve by another layer of inirection. Davi Wheeler VOLK abstractions: arch (gen/archs.xml) machines (gen/machines.xml) (U) 26 August / 19

9 Compatibility: the arch abstraction Architectures are harware features, escribe in an xml file with Arch name Compiler flags Alignment restrictions check name (efine in tmpl/volk cpu.tmpl.c) (U) 26 August / 19

10 Compatibility: the machine abstraction Machines are a collection of architectures that are foun together in real harware. Example ( neon ): generic neon softfp OR harfp ORC is optional (U) 26 August / 19

11 Compatibility: kernels an protokernels Kernel: the boy of a vectorize loop (kernels/volk/*.h) Proto-kernel: a specific implementation of a kernel (functions in kernels/volk/*.h or.s files in kernels/volk/asm/<arch>/) input signature output signature proto-kernel tag volk_32fc_magnitue_32f_u_neon_fancy_sweet volk namespace kernel alignment API: from your application call the ispatcher volk 32fc magnitue 32f(...) (U) 26 August / 19

12 (U) 26 August / 19

13 Compatibility: the profiler an ispatcher volk profile will run an time all proto-kernels for your machine Fastest proto-kernels per kernel are store in $HOME/.volk/volk config At run-time ispatcher loas volk config an runs what volk profile reporte as fastest (lib/volk rank archs.c) Dispatcher hanles selecting alignment an vali proto-kernels (U) 26 August / 19

14 Compatibility: putting it all together sp engineer buil system user kernels/volk/volk_32f_x2_ot_pro_32f.h #ifef LV_HAVE_NEON volk_32f_x2_ot_pro_32f_neon(...)... NEON machine #enif volk_32f_x2_ot_pro_32f(...) #ifef LV_HAVE_AVX volk_32f_x2_ot_pro_32f_avx(...) neon arch... #enif volk_32fc_x2_multiply_32fc(...) avx arch kernels/volk/volk_32fc_x2_multiply_32fc.h #ifef LV_HAVE_NEON volk_32fc_x2_multiply_32fc_neon(...) AVX machine libvolk.so gr-signals sse arch... #enif volk_32f_x2_ot_pro_32f(...) #ifef LV_HAVE_AVX volk_32fc_x2_multiply_32fc_avx(...)... volk_32fc_x2_multiply_32fc(...) #enif #ifef LV_HAVE_SSE volk_32fc_x2_multiply_32fc_sse(...)... #enif (U) 26 August / 19

15 A final note on compatibility: QA an Puppets VOLK QA reas function signatures to generate buffers an ranom input ata Arch-specific proto-kernels are compare to generic for correctness If VOLK QA cannot generate buffers for your signature you nee a puppet Puppets wrap your kernel in a VOLK QA-frienly form. See the rotatorpuppet for examples (U) 26 August / 19

16 Collaboration VOLK is a repository for efficient coe that people actually wrote (not the coe we wish they wrote) (U) 26 August / 19

17 Collaboration: VOLK for you volk motool: like gr motool, but for VOLK experiment with new archs A kernels (new heaer files) Hopefully contribute upstream (U) 26 August / 19

18 Parting Thoughts VOLK is a necessity cause by vectorization being very ifficult for compilers DSP esigners write coe specific to harware an wrap it insie VOLK Users call VOLK kernels when they are available After profiling your coe, create a VOLK kernel where it is neee Contribute VOLK kernels upstream for collaboration (U) 26 August / 19

19 Working Group Thursay at 3:00 PM Missing kernels/proto-kernels Arch-specific helper sub-libraries Buil issues General feeback (U) 26 August / 19

Unit 15. Building Wide Muxes. Building Wide Muxes. Common Hardware Components WIDE MUXES

Unit 15. Building Wide Muxes. Building Wide Muxes. Common Hardware Components WIDE MUXES 5. 5.2 Unit 5 Common Harware Components WIE MUXE 5.3 5.4 Builing Wie Muxes Builing Wie Muxes o far muxesonly have single bit inputs I is only -bit I is only -bit What if we still want to select between