Can a User Process Consume Kernel Mode CPU Without a Syscall? | Tanel Poder Consulting

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Can a User Process Consume Kernel Mode CPU Without a Syscall? | Tanel Poder Consulting

Yes!
Various traps like page faults may cause your user process to be switched into kernel codepath even when the process is minding its own business in the userspace. It just needs to do something that causes such a trap, like touch a new page of memory in its virtual memory address space, that hasn’t been “fully materialized” yet in the kernel memory structures.
For example, after starting up an Oracle database instance that uses a large amount of shared memory, there’s one process that burns CPU for a while: - Linux, Oracle, SQL performance tuning and troubleshooting - consulting & training.

https://tanelpoder.com/posts/user-process-consuming-kernel-cpu-without-a-syscall/