@Partha Sinha Welcome to Microsoft Q&A Forum, Thank you for posting your query here!
Performance issues occur in different operating systems or applications, and every issue requires a unique approach to troubleshoot. Most of these issues revolve around CPU, Memory, Networking, and input/output (I/O) as key locations where the issue occurs. Each of these areas generates different symptoms (sometimes simultaneously) and requires a different diagnosis and solution.
This article discusses high-CPU usage issues that occur on Azure Virtual Machines (VMs) that run the Windows operating system.
Troubleshoot Azure virtual machine performance on Linux or Windows
This looks more of a Windows OS specific issue than Azure, to isolate the issue you may try the following suggestions:
I understand that the PerfInsights has taken more than 3 hrs, if it generates the log, you may analyse the logs as outlined in the KB article How to use PerfInsights to diagnose high CPU or disk usage issues and further isolate the issue.
Troubleshoot High CPU usage by the "System" process
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