We also measure the CPU usage to different key events in the rendering of the page. SpeedCurve's focus is on the user experience and getting content in front of people as fast as possible, so we show you what the CPU is doing up till the page starts to render. This reflects CPU usage during the browser critical rendering path and can highlight various issues. If there's lots of CPU idle time then you're not delivering your resources efficiently. You want to get the CPU busy nice and early rendering the page, rather than sitting idle waiting for slow resources.
In the test below we see in the first pie chart that the CPU is spending a lot of time on layout up to the start render event, which is quite a different picture from the Fully Loaded CPU usage.
Over the last few years the web performance monitoring toolset has expanded dramatically with the introduction of many new services and products. There are two main types of web performance monitoring, uptime monitoring and real user monitoring. SpeedCurve focuses on a third which I like to call web performance benchmarking.