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Page Profiling gives good detail on what operations are slow in a page load. In addition, you can add debug level logging:
Set the package name com.atlassian.renderer.v2.components.MacroRendererComponent to DEBUG in Administration >> Logging and Profiling.
Download WikiMarkupParser.class, available from the attachments to this page. This will result in logs like:
2009-04-23 10:27:54,789 DEBUG [http-8080-1] [atlassian.renderer.v2.WikiMarkupParser] parse Entering macro rendering. Processed text: {spaces}
2009-04-23 10:27:55,768 DEBUG [http-8080-1] [atlassian.renderer.v2.WikiMarkupParser] parse Exiting macro text rendering. Total time: 979ms
2009-04-23 10:27:55,785 DEBUG [http-8080-1] [atlassian.renderer.v2.WikiMarkupParser] parse Entering macro rendering. Processed text: {create-space-button}
2009-04-23 10:27:55,857 DEBUG [http-8080-1] [atlassian.renderer.v2.WikiMarkupParser] parse Exiting macro text rendering. Total time: 72ms
2009-04-23 10:27:55,862 DEBUG [http-8080-1] [atlassian.renderer.v2.WikiMarkupParser] parse Entering macro rendering. Processed text: {recently-updated-dashboard:dashboard|showProfilePic=true}
2009-04-23 10:27:56,704 DEBUG [http-8080-1] [atlassian.renderer.v2.WikiMarkupParser] parse Exiting macro text rendering. Total time: 842ms
2009-04-23 10:27:56,707 DEBUG [http-8080-1] [atlassian.renderer.v2.WikiMarkupParser] parse Entering macro rendering. Processed text: {favpages:maxResults=10}
2009-04-23 10:27:56,889 DEBUG [http-8080-1] [atlassian.renderer.v2.WikiMarkupParser] parse Exiting macro text rendering. Total time: 182ms
To add the class:
In combination with page profiling, this should give good specifics on the amount of time various plugins take. You can also use this utility to Search Confluence for Uses of a Macro.
Experiment with the tips from the performance tuning page, or open an enhancement request about the specific macro. In some instances there is no resolution - you'll just be aware of the overhead of various macros.