Exchange Team blogged a few hints to troubleshoot cpu utilization in Exchange Server 2013.
In Exchange support we see a wide range of support issues. Few of them can be more difficult to troubleshoot than performance issues. Part of the reason for that is the ambiguity of the term "Performance Issue". This can manifest itself like anything from random client disconnects to database failovers or slow mobile device syncing. One of the most common performance issues we see are ones where the CPU is running higher than expected. "High CPU" can also be a bit of an ambiguous term as well. What exactly is high? How long does it occur? When does it occur? All of these are questions that have to be answered before you can really start getting to the cause of the issue. For example, say you consider ‘high’ to be 75% of CPU utilization during the day. Are you experiencing a problem, are databases inadequately balanced, or is the server just undersized? What about a 100% CPU condition? Does it happen for 10 seconds at a time or 10 minutes at a time? Does it only happen when clients first logon in the morning or after a failover? In this article I'll go into some common causes of high CPU utilization issues in Exchange 2013 and how to troubleshoot them.
Read more at source: http://blogs.technet.com/b/exchange/archive/2015/04/30/troubleshooting-high-cpu-utilization-issues-in-exchange-2013.aspx