SMON allows for the periodic collection of performance data such as CPU utilization, memory, work process utilization and samples, request queue lengths, and more.
Learn how to configure and schedule SMON: SAP Note 2651881 - How to configure SMON for performance monitoring and analysis
For other information related to SMON, see All About SMON
SMON replaces the older snapshot tool /SDF/MON. We recommend using SMON when possible.
For information on /SDF/MON see SAP Note 2383809 - "How to use the SDF/MON tool to analyse performance issues"