new: cpu load

content/OS/CPU/CPU Load.md

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+---
+Author:
+  - Xinyang YU
+Author Profile:
+  - https://linkedin.com/in/xinyang-yu
+tags:
+  - os
+Creation Date: 2024-12-15, 14:51
+Last Date: 2024-12-15T15:14:29+08:00
+References: 
+draft: 
+description: CPU load measures the number of processes using or waiting for the CPU at a given time, with optimal load typically around 0.7 per CPU core to handle real-world spikes. On Unix-like systems, high load may indicate I/O bottlenecks rather than CPU contention, leading to increased response times and performance delays.
+---
+## Abstract
+---
+- CPU load measures the **number of processes that are either using or waiting for the [[CPU]]** at a specific time
+
+>[!question] What does the CPU Load number mean?
+> If the load is low, [[Process (进程)|processes]] can access the CPU without waiting. If the load exceeds the number of CPUs, processes form a queue, leading to [[#CPU Contention]]. For a single-CPU system, a **load < 1** indicates no waiting.
+
+>[!important] Guidelines for optimal load
+> A steady load of `1` per [[CPU#CPU Core|core]] ensures optimal CPU utilisation.
+> 
+> However, to accommodate real-world spikes, aiming for a load of **0.7 per CPU** is more practical.
+
+>[!attention] Unix system load calculation caveat
+> On [[Unix#Unix-like|Unix-like systems]], high load might indicate **I/O bottlenecks** rather than actual CPU contention. 
+> 
+> The load calculation includes **processes blocked in [[IO Device#IO Operation]]** (e.g., waiting for disk or network), which can inflate load numbers even if the CPU isn't fully utilised.
+> 
+> For example, A **15-minute load average of 37**, combined with CPU usage not being at **100%**, strongly suggests an **I/O bottleneck** or processes waiting on resources other than CPU (like disk, network, or memory contention).
+
+
+### CPU Contention
+- Too many [[Process (进程)|processes]] competing for [[CPU|CPU resources]]
+
+>[!attention] Increased response time
+> Processes experience **longer wait times for CPU access**, leading to significant delays, such as slower application performance.
+
+
+## References
+---
+- [CPU Usage vs Load. Don’t confuse the two! | by Benny Ou | ESTL Lab Notes](https://estl.tech/cpu-usage-vs-load-ecca22287b21)