I think it's like this: Each line with "###" in bold is a system call, and the preceding non-bold lines show the corresponding backtrace (sequence of nested act

I think it's like this: Each line with "###" in bold is a system call, and the preceding non-bold lines show the corresponding backtrace (sequence of nested active function calls at the time of the system call). A system call is expensive, but not as expensive as a context switch between two user processes.