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Of the user, system, and idle readings provided by "top", which would reflect the time spent in a blocking system call?

I have read that blocking disk i/o calls are reflected as idle time, but not so for blocking network i/o calls. But then where?

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Not CPU time is spent while code waits for some event to occur so just like with I/Os, a blocking network system call is essentially idle time.

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It is shown as wait (wa) in top. That does not reflect the involved wait time but the CPU effort in dealing with the operation.

If a process were to read a large file from a slow disk, the kernel's scheduler would have to more frequently assign CPU to deal with the I/O operation and would therefore also waste scheduler time in dealing with it.

Unfortunately, even kernel developers can not give a more straight-forward answer because the real wait time does not require CPU, but dealing with it does.

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