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AVX

Architecture referenceFeex

AVX, wey be Advanced Vector Extensions, dey add vector programming model with YMM register dem and VEX-encoded instruction dem, including 256-bit floating-point operation dem. Both processor support and operating-system state management dey required.

Wetin you need know

AVX, wey be Advanced Vector Extensions, dey add vector programming model with YMM register dem and VEX-encoded instruction dem, including 256-bit floating-point operation dem. Both processor support and operating-system state management dey required.

How e dey work

AVX dey extend vector register dem reach 256 bits, with each YMM register lower 128 bits overlapping e XMM register. Many instruction dem dey use three-operand shape, wey dey allow di destination make e different from di input dem. 256-bit vector fit hold 8 single-precision or 4 double-precision floating-point value dem, but instruction dem dey different for dia operand type dem and behavior.

Where e dey useful

Numeric loop fit add several independent floating-point value dem using one vector instruction. Di compiler or library must generate dat code and arrange load dem, alignment, tail dem and dependency dem well. AVX no dey automatically spread any kind program across multiple core dem, and 256-bit integer operation dem need person to check di correct extension instead make you assume AVX2.

How to check support and enablement

Check CPUID.01H:ECX AVX bit 28, XSAVE bit 26 and OSXSAVE bit 27. Na only after you confirm OSXSAVE make software use XGETBV with ECX=0, den verify say XCR0 bit 1 and 2 enable XMM and YMM state. Use maintained runtime dispatcher instead of running AVX as experiment to detect feature.

Di program must contain correct implementation and select am at runtime. Hardware enumeration, OS-enabled register state and di binary compiled baseline na separate check dem. Virtual machine fit deliberately show fewer feature dem pass e host, and container no dey add instruction to di host CPU.

Wetin di feature no dey guarantee

AVX support alone no mean AVX2, FMA, F16C, AVX-VNNI or AVX-512. Vector width no dey talk how many cycle instruction dey take. Virtual machine fit show smaller instruction set pass di physical host.

Compatibility and performance inside real life

Measure di full workload with representative data. Wider vector dem fit reduce instruction count while memory traffic, synchronization or conversion cost dem remain di same. Instruction latency, throughput and power behavior depend on di exact microarchitecture and operating condition dem.

Practical verification checklist

  1. Record di exact processor or platform model plus di application, OS and runtime version dem wey dey involve. Make you keep di exact word dem wey di error or requirement use.
  2. Check di manufacturer reference for dat exact model, den inspect di real capability and enabled state inside di environment where di program dey run.
  3. Compare every single requirement of di binary or backend wey you choose. Name wey resemble am, alias, or broad technology label no reach.
  4. Confirm say di application select di implementation wey dem intend. Use di diagnostics wey dem document and supported fallback if requirement dem no complete.
  5. Make only one supported change at a time, den run di same workload again. Keep di original configuration and recovery way ready.

If dem list di feature but software no fit use am

Start from di exact component wey dey fail. Hardware database dey describe capability wey dem record; di operating system or hypervisor fit show different real environment. If illegal-instruction error happen, you still need to check di exact instruction wey cause di fault and di binary build, because corrupt file or anoda instruction wey no dey supported fit give di same kind problem.

Install di application, driver or runtime version wey get support for dat exact platform, and use di vendor documented baseline or fallback build if e need am. Software update no fit create instruction wey di processor no get. Firmware and security-policy change dem suppose follow di system manufacturer procedure and recovery plan, no be just any common optimization advice.

Sources and scope of dis explanation

Intel 64 and IA-32 Architectures Software Developer's Manual · Linux kernel: using XSTATE features in user space

Dis reference dem establish architectural behavior and software requirement dem. Dem no dey independently verify every feature value for any linked hardware model page. For model support, use dat page manufacturer evidence and check di active system configuration. Dis article no supply benchmark, certification or independent review date.

Sources and verification

Editorial ownership: Feex. No independent review date dey recorded. How we dey do research.

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