Discover the Power of AVX in x86 Architecture

Discover the Power of AVX in x86 Architecture

Table of Contents

1. Introduction to AVX
2. AVX and Hardware Requirements
3. AVX Registers
4. AVX Instructions
5. Non-destructive Nature of AVX
6. AVX Programming Example
7. Detecting AVX Support with cpuid
8. testing AVX Support
9. Porting an Algorithm from SSE to AVX
10. Conclusion

Introduction to AVX

AVX (Advanced Vector Extensions) is an extension to the x86 architecture that provides advanced vector processing capabilities. Unlike SSE, AVX is only available on newer CPUs from 2012 onwards. It offers a massive improvement to the x86 architecture, with 256-bit wide registers, twice the width of SSE registers. AVX requires both hardware and OS support, making it necessary to have compatible CPUs and updated operating systems.

AVX and Hardware Requirements

To utilize AVX, it is crucial to have CPUs that support AVX instructions. CPUs like Sandy Bridge, Ivy Bridge, and AMD Bulldozer chips offer AVX support. Additionally, the operating system must also support AVX, requiring updated service packs for Windows 7 or Windows 8, which natively support AVX.

AVX Registers

AVX introduces 16 new registers, named "ymm0" through "ymm15." Each register is 256 bits wide and is also an alias to the 16 SSE registers. AVX registers can be used for different sized data elements, mostly focusing on floating-point values. For each register, there are various configurations for packed singles, packed doubles, or other data types.

AVX Instructions

AVX instructions are similar to SSE instructions, with most SSE instructions having an AVX version. AVX instructions have the same mnemonic as their SSE counterparts but with a "v" prefix. AVX instructions offer twice the precision due to the 256-bit wide registers. There are also new AVX instructions, including broadcasting, masked moves, extraction, insertion, shuffling, and zeroing instructions.

Non-destructive Nature of AVX

Unlike most x86 instructions that are destructive, AVX instructions operate in a non-destructive manner. They have three operands: two source operands and one destination operand. The results of the operation are stored in the destination operand, while the source operands remain unchanged. This non-destructive nature allows for more flexibility in calculations and reduces memory overhead.

AVX Programming Example

To demonstrate AVX programming, we will create a simple CPUID detection program. By using the CPUID instruction and checking the 28th bit of ECX after function number 1, we can determine if the CPU supports AVX. This function will help us ensure AVX compatibility before proceeding with AVX programming tasks.

Detecting AVX Support with cpuid

To detect AVX support, we will use the CPUID instruction with function number 1. Clearing EAX and calling CPUID will provide us with the necessary information. By checking the 28th bit of ECX, which corresponds to AVX support, we can set a flag indicating AVX compatibility. This method offers a quicker way to detect AVX support compared to other approaches.

Testing AVX Support

To test AVX support, we will implement the AVX detection function Mentioned earlier. By calling the function and checking its return value, we can determine if AVX is supported on the current CPU. If AVX is supported, we can proceed with AVX programming tasks; otherwise, we need to consider using a different CPU or updating the hardware.

Porting an Algorithm from SSE to AVX

A practical way to introduce AVX programming and showcase its benefits is by porting an algorithm from SSE to AVX. In this example, we will take an algorithm that utilizes SSE instructions and modify it to leverage the advanced capabilities of AVX. This process will demonstrate the similarities between SSE and AVX instructions and highlight the advantages of using AVX for improved performance.

Conclusion

AVX is an exciting extension to the x86 architecture that offers advanced vector processing capabilities. It provides wider registers, non-destructive operations, and improved precision compared to SSE. Utilizing AVX instructions can greatly enhance performance in applications that heavily rely on vector operations. However, it is essential to ensure hardware and OS compatibility before engaging in AVX programming.