hi,
in system v there are no worker process.why in systemd we have worker process?
a worker process is used by an user mode process when this process work in kernel mode?
during the process life a process can run in user mode or kernel mode.in kernel mode the process has elevated privileges.right?

I don't know which processes you mean, but the difference between System V initialization and systemd is that systemd does much more than just starting and stopping services.
"Elevated privileges" is usually understood as "superuser privileges". The process doesn't change its ID to superuser when it enters the kernel. Instead, the CPU changes state so that it can execute privileged instructions and access protected memory areas.

On Slackware with KDE, which most decidedly does not use SystemD but rather uses a BSD-style init system, there are "kworker" processes.

Also, I just fired up my VM of Devuan (which was due an update anyway); I'm using the KDE desktop and I found a number of "kworker" processes.

Consequently, I think it would help if you would provide a list of the "worker" processes to which you refer.

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These are kernel processes, i.e. all their code resides in the kernel. They should be marked like this: [kworker]. I believe they perform various asynchronous tasks, perhaps garbage collection and the like, and indeed have nothing to do with systemd or any other service initialization or management framework.

Here is a (very technical and deep) description: https://www.kernel.org/doc/Documenta.../workqueue.rst. Google knows about much more documentation.

If this is what OP means by "worker", I can answer this question:
Only if you use "used" in a very very loose way. In the sense of "user mode processes use the kernel to accomplish tasks".

hi,
i refer to kworker


ps -ef|more
UID PID PPID C STIME TTY TIME CMD
root 1 0 1 02:50 ? 00:00:01 /usr/lib/systemd/systemd --swi
tched-root --system --deserialize 22
root 2 0 0 02:50 ? 00:00:00 [kthreadd]
root 3 2 0 02:50 ? 00:00:00 [ksoftirqd/0]
root 4 2 0 02:50 ? 00:00:00 [kworker/0:0]
root 5 2 0 02:50 ? 00:00:00 [kworker/0:0H]
root 6 2 0 02:50 ? 00:00:00 [kworker/u256:0]

so a process run in user mode and when need kernel,it runs in kernel mode.right?

A process switches to kernel mode when it makes a system call.