The Grand Unified Theory of Documentation
– David Laing

There is a secret that needs to be understood in order to write good software documentation: there isn’t one thing called documentation, there are four.

They are: tutorials, how-to guides, technical reference and explanation. They represent four different purposes or functions, and require four different approaches to their creation. Understanding the implications of this will help improve most documentation - often immensely.

• Tutorials - Learning oriented
• How-to guides - Problem oriented
• Explanation - Understanding oriented
• Reference - Information oriented

This page describes Pressure Stall Information (PSI), how to use it, tools and components that work with PSI, and some case studies showing how PSI is used in production today for resource control in large data centers.
Overview

PSI provides for the first time a canonical way to see resource pressure increases as they develop, with new pressure metrics for three major resources—memory, CPU, and IO.

These pressure metrics, in conjunction with cgroup2 and other kernel and userspace tools described below, allow you to detect resource shortages while they’re developing, and respond intelligently—by pausing or killing non-essentials, reallocating memory in the system, load shedding, or other actions.

PSI stats are like barometers that provide fair warning of impending resource shortages, enabling you to take more proactive, granular, and nuanced steps when resources start becoming scarce.

See the PSI git repo for additional information.

These calculators require the use of Javascript enabled and capable browsers. Compare information of original equipment tire size and alternate after market tire sizes. There are two flavors, one for U.S. designation tires and one for metric TRX designation tires. All calculations are designed to round up. Calculations are to be treated as approximate only, due to possible and probable variations in how tires are manufactured. The information in the Required area is needed to perform the comparison. The tire tread width, sidewall (aspect) ratio, and wheel rim diameter from each of the two tires to be compared, along with a speedometer reading used to compute the effect the after market tire size has on your speedometer's accuracy. The following is an example to help to decode a tire size like 195/70R15. The 195 is the tire width in millimeters, measured from the bottom of the bead to the bottom of the bead, the 70 is the sidewall aspect ratio, the ratio of sidewall height to tire width at the tread (indicating that the sidewall height is 70% of the tread width), and the 15 is the wheel rim diameter in inches. After the data entry of the required information, click on the Compare U.S. Tires button in the top calculator or Compare Metric Tires in the lower calculator to have the selected tire sizes compared. Adjusted Speedometer Reading is what speed the car will need to go if using the after market tires, to be traveling at the same speed if the car had the original tires on. It is an adjustment faster or slower from the original speed. Please select from U.S. or Metric comparisons.