I'm a major fan of Microsoft OneDrive, formerly known as SkyDrive. I've used it since the days of its even earlier name, Windows LiveMesh.
A few times in recent months I've had issues where the SkyDrive/OneDrive sync process hogs loads of CPU cycles, with the Search Indexer process also having the same problem.
After some more digging last night, and not wanting to consider a re-install of the OS (Windows 8.1 Pro), I came across a tool Microsoft released ages ago to help troubleshoot sync issues with OneDrive. Needless to say, this isn't exactly easy to find, but after a good hour of scanning, it fixed some file security and access faults, then prompted me to reset OneDrive. The reset forces OneDrive to do a full file sync and for me took another hour, but once complete, it re-downloaded the files to my laptop and so far the CPU usage is back to normal - it's really worth trying out if you have similar issues!
The tool can be found on this page:
http://windows.microsoft.com/en-gb/windows-8/troubleshoot-sync-problems
Click the link titled 'Run the troubleshooter' which prompts download of a CAB file, which is the troubleshooter software itself.