Droidcon ndk cpu_architecture_optimization
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The document discusses optimizing NDK projects to support multiple CPU architectures. It covers topics such as setting compiler options for ARM and x86, using code paths and preprocessor macros to optimize for different architectures, and key differences between ARM and x86 like memory alignment. The document recommends approaches like using the Android NDK build system and Cpufeatures API to optimize code for multiple architectures and publishing either a fat binary or multiple APKs to distribute apps broadly.
Droidcon ndk cpu_architecture_optimization
- 1. Optimizing NDK projects for multiple CPU architectures Alexander Weggerle Technical Consultant Engineer Intel Software and Services Group
- 2. Agenda • Compatibility • Compiler options • Code paths • Differences between ARM and x86 • Publishing Copyright© 2012, Intel Corporation. All rights reserved. *Other brands and names are the property of their respective owners.
- 3. Introduction • Performance critical apps are popular • Games • Real time multimedia • Augmented reality • Users are sensitive • Don’t accept lags • Fluid animations • Minimal load time Optimization is important Copyright© 2012, Intel Corporation. All rights reserved. *Other brands and names are the property of their respective owners.
- 4. Compatibility “I want my app to run on all architectures” • You already done for Java & HTML • NDK based apps usually just needs a recompilation APP_ABI := all Application.mk Copyright© 2012, Intel Corporation. All rights reserved. *Other brands and names are the property of their respective owners.
- 5. Agenda • Compatibility • Compiler options • Code paths • Differences between ARM and x86 • Publishing Copyright© 2012, Intel Corporation. All rights reserved. *Other brands and names are the property of their respective owners.
- 6. Target compiler options • NDK-build system Android.mk file evaluated for each architecture • Variable TARGET_ARCH_ABI describes actual architecture TARGET_ARCH_ABI ifeq ($(TARGET_ARCH_ABI),x86) LOCAL_CFLAGS := -mtune=atom -mssse3 x86 endif armeabi ifeq ($(TARGET_ARCH_ABI),armeabi-v7a) LOCAL_CFLAGS := -march=armv7-a armeabi-v7a Endif mips Android.mk Copyright© 2012, Intel Corporation. All rights reserved. *Other brands and names are the property of their respective owners.
- 7. Recommended Compiler options (x86) • -mtune=atom • Out of Order scheduling • -march=atom • movbe instruction • Code is only guaranteed to run on Atom. – Might not run on emulator or other CPUs • -ansi-alias / -restrict / -no-prec-div Copyright© 2012, Intel Corporation. All rights reserved. *Other brands and names are the property of their respective owners.
- 8. Agenda • Compatibility • Compiler options • Code paths • Differences between ARM and x86 • Publishing Copyright© 2012, Intel Corporation. All rights reserved. *Other brands and names are the property of their respective owners.
- 9. Multiple Code Paths • Different reasons for multiple code paths • Optimizing for multiple architectures • Single Instruction Multiple Data (SIMD) • Assembly kernels • Memory alignment • Instruction set support Copyright© 2012, Intel Corporation. All rights reserved. *Other brands and names are the property of their respective owners.
- 10. Multiple Code Paths Compiler macros • Directly inside source code • No runtime overhead • Works with all build configurations #ifdef __i386__ strlcat(buf, "__i386__", sizeof(buf)); #endif #ifdef __arm__ strlcat(buf, "__arm__", sizeof(buf)); #endif #ifdef _MIPS_ARCH strlcat(buf, "_MIPS_ARCH", sizeof(buf)); #endif source.c Copyright© 2012, Intel Corporation. All rights reserved. *Other brands and names are the property of their respective owners.
- 11. Multiple Code Paths Make system • Make system will select source file depending on architecture • No runtime overhead arch_x86.cpp const char *getTarget (); arch_arm.cpp arch.h cpufeaturestest.cpp const char *getTarget (); const char *getTarget (); printf(“%s”, getTarget()); arch_default.cpp const char *getTarget (); Copyright© 2012, Intel Corporation. All rights reserved. *Other brands and names are the property of their respective owners.
- 12. Multiple Code Paths Cpufeatures API • Checks for architecture and special CPU features • Uses compiler macros + runtime detection internally • Small runtime overhead Copyright© 2012, Intel Corporation. All rights reserved. *Other brands and names are the property of their respective owners.
- 13. Agenda • Compatibility • Compiler options • Code paths • Differences between ARM and x86 • Publishing Copyright© 2012, Intel Corporation. All rights reserved. *Other brands and names are the property of their respective owners.
- 14. Porting Native (C/C++) Android* Apps to x86 http://software.intel.com/en-us/articles/ndk-android-application-porting- methodologies/ Native Apps • Optimized NDK for Intel Atom based devices available on http://developer.android.com/sdk/nd k/index.html since July’11. • For most apps, changing the make file and a recompile should be sufficient to port to Intel Atom devices. • If ARM-specific features are used, Intel SSE equivalents should be added (build flag) • Developer recompiles, re-packages and publishes. Copyright© 2012, Intel Corporation. All rights reserved. *Other brands and names are the property of their respective owners.
- 15. ARM* NEON to Intel® SSE • Single Instruction Multiple Data (SIMD) • Most ARM NEON functions have a 1:1 equivalent in Intel® SSE • Intel provides C++ header file to do the mapping // VADD.I8 d0,d0,d0 int8x8_t vadd_s8(int8x8_t a, int8x8_t b); #ifdef USE_MMX #define vadd_s8 _mm_add_pi8 //MMX #else #define vadd_s8 _mm_add_epi8 #endif neonvssse.h Copyright© 2012, Intel Corporation. All rights reserved. *Other brands and names are the property of their respective owners.
- 16. Differences between ARM and x86 Alignment • ARM uses aligned, x86 uses packed memory struct TestStruct ARM { int mVar1; long long mVar2; int mVar3; }; x86 • Compiler parameter helps to workaround -malign-double Copyright© 2012, Intel Corporation. All rights reserved. *Other brands and names are the property of their respective owners.
- 17. Agenda • Compatibility • Compiler options • Code paths • Differences between ARM and x86 • Publishing Copyright© 2012, Intel Corporation. All rights reserved. *Other brands and names are the property of their respective owners.
- 18. Market Fat binary • Include all binaries into one apk libs/armeabi Source ndk-build apkbuilder libs/armeabi- v7a … libs/x86 • Device removes incompatible libs at installation Copyright© 2012, Intel Corporation. All rights reserved. *Other brands and names are the property of their respective owners.
- 19. Market Multiple APKs • Support for different … • Texture formats • Screen sizes and densities • Platform versions • CPU architectures • Saves bandwidth and space while installation Copyright© 2012, Intel Corporation. All rights reserved. *Other brands and names are the property of their respective owners.
- 20. Conclusion & Call to action • NDK provides plenty of mechanisms to differentiate between architectures • Recompile your NDK based app with APP_ABI := all Copyright© 2012, Intel Corporation. All rights reserved. *Other brands and names are the property of their respective owners.
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- 22. Legal Disclaimer & Optimization Notice INFORMATION IN THIS DOCUMENT IS PROVIDED “AS IS”. NO LICENSE, EXPRESS OR IMPLIED, BY ESTOPPEL OR OTHERWISE, TO ANY INTELLECTUAL PROPERTY RIGHTS IS GRANTED BY THIS DOCUMENT. INTEL ASSUMES NO LIABILITY WHATSOEVER AND INTEL DISCLAIMS ANY EXPRESS OR IMPLIED WARRANTY, RELATING TO THIS INFORMATION INCLUDING LIABILITY OR WARRANTIES RELATING TO FITNESS FOR A PARTICULAR PURPOSE, MERCHANTABILITY, OR INFRINGEMENT OF ANY PATENT, COPYRIGHT OR OTHER INTELLECTUAL PROPERTY RIGHT. Software and workloads used in performance tests may have been optimized for performance only on Intel microprocessors. Performance tests, such as SYSmark and MobileMark, are measured using specific computer systems, components, software, operations and functions. Any change to any of those factors may cause the results to vary. You should consult other information and performance tests to assist you in fully evaluating your contemplated purchases, including the performance of that product when combined with other products. Copyright © , Intel Corporation. All rights reserved. Intel, the Intel logo, Xeon, Core, VTune, and Cilk are trademarks of Intel Corporation in the U.S. and other countries. Optimization Notice Intel’s compilers may or may not optimize to the same degree for non-Intel microprocessors for optimizations that are not unique to Intel microprocessors. These optimizations include SSE2, SSE3, and SSSE3 instruction sets and other optimizations. Intel does not guarantee the availability, functionality, or effectiveness of any optimization on microprocessors not manufactured by Intel. Microprocessor-dependent optimizations in this product are intended for use with Intel microprocessors. Certain optimizations not specific to Intel microarchitecture are reserved for Intel microprocessors. Please refer to the applicable product User and Reference Guides for more information regarding the specific instruction sets covered by this notice. Notice revision #20110804 22 Intel Confidential Copyright© 2012, Intel Corporation. All rights reserved. 09.04.2013 *Other brands and names are the property of their respective owners.