quick note USE method

Author: ntk148v

golang

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+# USE method
+
+Source: <https://www.brendangregg.com/usemethod.html>
+
+## 1. Summary
+
+> [!important]
+> For every resource, check utilization, saturation, and errors.
+
+Terminology definitions:
+- resource: all physical server functional components (CPUs, disks, busses, ...).
+- utilization: the average time that the resource was busy servicing work.
+- saturation: the degree to which the resource has extra work which it can't service, often queued
+- errors: the count of error events.
+
+The metrics are usually expressed in the following terms:
+- utilization: as a percent over a time interval. eg, "one disk is running at 90% utilization".
+- saturation: as a queue length. eg, "the CPUs have an average run queue length of four".
+- errors: scalar counts. eg, "this network interface has had fifty late collisions".
+
+A burst of high utilization can cause saturation and performance issues, even though utilization is low when averaged over a long interval.
+
+## 2. Resource list
+
+- CPUs: sockets, cores, hardware threads (virtual CPUs)
+- Memory: capacity
+- Network interfaces
+- Storage devices: I/O, capacity
+- Controllers: storage, network cards
+- Interconnects: CPUs, memory, I/O
+
+The USE Method is most effective for resources that suffer performance degradation under high utilization or saturation, leading to a bottleneck. Caches improve performance under high utilization.
+
+## 3. Suggested Interpretations
+
+The USE Method helps you identify which metrics to use. After learning how to read them from the operating system, your next task is to interpret their current values.
+
+The following are some general suggestions for interpreting metric types:
+
+- **Utilization**: 100% utilization is usually a sign of a bottleneck (check saturation and its effect to confirm). High utilization (eg, beyond 70%) can begin to be a problem for a couple of reasons:
+  - When utilization is measured over a relatively long time period (multiple seconds or minutes), a total utilization of, say, 70% can hide short bursts of 100% utilization.
+  - Some system resources, such as hard disks, cannot be interrupted during an operation, even for higher-priority work. Once their utilization is over 70%, queueing delays can become more frequent and noticeable. Compare this to CPUs, which can be interrupted ("preempted") at almost any moment.
+- **Saturation**: any degree of saturation can be a problem (non-zero). This may be measured as the length of a wait queue, or time spent waiting on the queue.
+- **Errors**: non-zero error counters are worth investigating, especially if they are still increasing while performance is poor.
+
+## 4. Strategy
+
+![](https://www.brendangregg.com/USEmethod/usemethod_flow.png)