Performance Monitor can be used to see the % processor time and # of context switches. The context switch counts are available in either:
- System\Context Switches/sec counter reports system wide context switches.
- Thread(_Total)\Context Switches/sec counter reports the total numberof context switches generated per second by all threads
Context switch overhead is low but if you see a much higher number at the same time as % processor time spikes then you can start troubleshooting what is occurring at that time. Other counters can help with narrowing down what the problem might be - for example Processor Queue Length.
Ref: TechNet Monitoring Context Switches
As well from another article on Context Switches:
You can determine whether context switching is excessive by comparing it with the value of Processor\% Privileged Time. If this counter is at 40 percent or more and the context-switching rate is high, then you can investigate the cause for high rates of context switches.