Learn about Large System Extensions
Introduction
Introduction to Large System Extensions
Deploy an example C program
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About this Learning Path

Skill level:  Introductory
Reading time:  30 min
Last updated:  29 Sep 2026
Skill level:
  Introductory
Reading time:
  30 min
Last updated:
  29 Sep 2026
Author:Jason Andrews, Arm
Arm IP:Neoverse
Tags: Performance and Architecture Arm AGI CPU AWS Graviton Microsoft Azure Cobalt Google Axion Oracle Cloud Infrastructure (OCI) Ampere Compute Linux GCC Runbook
Author:
  • Jason Andrews, Arm
Arm IP:
Neoverse
Tags:
Performance and Architecture Arm AGI CPU AWS Graviton Microsoft Azure Cobalt Google Axion Oracle Cloud Infrastructure (OCI) Ampere Compute Linux GCC Runbook

Who is this for?

This is an introductory topic for software developers who want to learn about Large System Extensions (LSEs) and use them in an application.

What will you learn?

After completing this Learning Path, you'll be able to perform the following tasks:

  • Understand LSEs.
  • Find out if an application uses LSE.

Prerequisites

Before starting, you'll need the following prerequisites:

  • Access to an AWS Graviton-based instance, an Arm AGI CPU platform, or other Arm Linux computers with LSE support

Summary

AI-assisted

This summary was drafted with an approved AI-assisted workflow and reviewed by Arm contributors before publication. Human technical review remains part of the process so the final page reflects engineering rigor, accuracy, and Arm editorial standards.

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You’ll explore how LSEs support atomic operations on many-core systems. First, you’ll create a C program that uses C11 threads and standard atomics for concurrent updates, then compile and run it on Arm Linux. You’ll compare atomic and non-atomic counters under contention and inspect the compiled output. Finally, you’ll verify whether your compiler generated LSE instructions for the target system.

Frequently asked questions

AI-assisted

These FAQs were drafted with an approved AI-assisted workflow and reviewed by Arm contributors before publication. Human technical review remains part of the process so the final page reflects engineering rigor, accuracy, and Arm editorial standards.

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Where should I save the example and which headers does it need?
Save the program as atomic.c. Include stdio.h, threads.h, and stdatomic.h.
How many threads and iterations does the example use?
You’ll create 10 threads, with each thread performing 1,000 increments of both the non-atomic and atomic counters.
What result should I expect when I run the program?
Confirm that the atomic counter reports the total increments across all threads. Your non-atomic counter can report a different value because concurrent updates create data races.
How do I verify whether the compiler generated LSE instructions?
Run the objdump command and check its count of LSE atomic instructions. You can also inspect the disassembly for instructions such as ldaddal.
How can I check whether my Arm-based Linux system supports LSE?
Run sudo dmesg | grep LSE and look for a message that reports detected LSE atomic instructions. You can also run lscpu | grep Flags. The atomics flag indicates LSE support.
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