identify the cause of high cpu utilization via xperf

1. Install xperf. Now xperf is in windows SDK. The setup file is wpt_x64.exe for amd64.

2. Start tracing
xperf -on latency -stackwalk Profile

3. After a while, stop tracing and generate trace file trace.etl.
xperf -d trace.etl

4. analyze the result. You need to provide pdb file to show the function name.
xperf trace.etl

As you can see sal_usleep() is the culprit and takes most of CPU time.

After we fix sal_usleep(), the CPU utilization drops significantly.

Another powerful feature of xperf is stack walking. It will output call stacks of a function. More information can be find here (stack walking) and here (enable stack walking on x64).