Home Backend Development C++ When Should You Use _mm_sfence, _mm_lfence, and _mm_mfence?

When Should You Use _mm_sfence, _mm_lfence, and _mm_mfence?

Nov 15, 2024 pm 02:44 PM

When Should You Use _mm_sfence, _mm_lfence, and _mm_mfence?

When Should You Use _mm_sfence, _mm_lfence, and _mm_mfence?

Multi-threaded programming introduces concurrency-related complexities, necessitating mechanisms to maintain data integrity and synchronization. Intel's intrinsics library provides several functions, including _mm_sfence, _mm_lfence, and _mm_mfence, to control memory ordering in x86 architectures.

Memory Ordering in x86

x86 CPUs have a strongly ordered memory model, but C and C have weaker ones. Hence, additional precautions are required to ensure proper memory ordering and prevent data corruption or race conditions.

_mm_sfence

_mm_sfence is primarily used after non-temporal (NT) stores (_mm_stream_*) to prevent speculative reordering. NT stores are weakly ordered, meaning they can appear to occur out of order relative to other memory operations. _mm_sfence creates a barrier that ensures subsequent memory operations become globally visible after the NT stores are committed to memory.

_mm_lfence

_mm_lfence is rarely used as a load fence. It only has relevance when loading from Write-Combining (WC) memory regions, such as video RAM. _mm_lfence can prevent execution of subsequent instructions until it retires, which can be useful for microbenchmarking.

_mm_mfence

_mm_mfence provides sequential consistency, ensuring subsequent loads cannot read values until after preceding stores become globally visible. It can be useful if you implement your custom version of std::atomic or need to explicitly control memory ordering for operations that would otherwise be speculative.

Summary

  • Use _mm_sfence after NT stores to prevent data corruption and race conditions.
  • Avoid _mm_lfence for load ordering unless specifically working with WC memory regions.
  • _mm_mfence offers sequential consistency but may be less efficient than locked atomic read-modify-write operations.
  • Consider using C 11 std::atomic or C11 stdatomic for memory synchronization, as they provide a more convenient and optimized approach.

The above is the detailed content of When Should You Use _mm_sfence, _mm_lfence, and _mm_mfence?. For more information, please follow other related articles on the PHP Chinese website!

Statement of this Website
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn

Hot Article Tags

Notepad++7.3.1

Notepad++7.3.1

Easy-to-use and free code editor

SublimeText3 Chinese version

SublimeText3 Chinese version

Chinese version, very easy to use

Zend Studio 13.0.1

Zend Studio 13.0.1

Powerful PHP integrated development environment

Dreamweaver CS6

Dreamweaver CS6

Visual web development tools

SublimeText3 Mac version

SublimeText3 Mac version

God-level code editing software (SublimeText3)

What are the types of values ​​returned by c language functions? What determines the return value? What are the types of values ​​returned by c language functions? What determines the return value? Mar 03, 2025 pm 05:52 PM

What are the types of values ​​returned by c language functions? What determines the return value?

Gulc: C library built from scratch Gulc: C library built from scratch Mar 03, 2025 pm 05:46 PM

Gulc: C library built from scratch

C language function format letter case conversion steps C language function format letter case conversion steps Mar 03, 2025 pm 05:53 PM

C language function format letter case conversion steps

What are the definitions and calling rules of c language functions and what are the What are the definitions and calling rules of c language functions and what are the Mar 03, 2025 pm 05:53 PM

What are the definitions and calling rules of c language functions and what are the

Where is the return value of the c language function stored in memory? Where is the return value of the c language function stored in memory? Mar 03, 2025 pm 05:51 PM

Where is the return value of the c language function stored in memory?

distinct usage and phrase sharing distinct usage and phrase sharing Mar 03, 2025 pm 05:51 PM

distinct usage and phrase sharing

How do I use algorithms from the STL (sort, find, transform, etc.) efficiently? How do I use algorithms from the STL (sort, find, transform, etc.) efficiently? Mar 12, 2025 pm 04:52 PM

How do I use algorithms from the STL (sort, find, transform, etc.) efficiently?

How does the C   Standard Template Library (STL) work? How does the C Standard Template Library (STL) work? Mar 12, 2025 pm 04:50 PM

How does the C Standard Template Library (STL) work?

See all articles