Performance Tuning ETL
For SSIS you can implement logging on the packages.  A good place to start looking would be at the ProcessInput and PrimeOutput steps of the components within the packages.  The PipelineComponentTime event will be useful to check for these steps, as it records the time spent in each of them.  You can read more about logging for SSIS here.

For SSAS you can use Extended Events to monitor the performance while the processing is being done.  The ProgressReportEnd and ResourceUsage events are two that you may want into look into examing during the times the cubes are processed, and well as the RequestProcessBegin and RequestProcessEnd events.  This link will further outline the use of Extended Events in SSAS.