Re: Some newbie questions

[fche at redhat dot com (Frank Ch. Eigler)]

avi wrote:

> [...]
> My load indeed calls epoll_wait() at a high rate, with zero timeout.

OK.  That's an unusual and cpu-saturating method.  Without systemtap
active, the code must be doing millions of syscalls per second.  Are
you sure there's no better way?


> But now it's completely dominated by tracing overhead.
> [...]
>                |          |--48.48%--task_utrace_struct
>                |          | |--25.21%--utrace_report_syscall_entry
>                |          |          | syscall_trace_enter_phase2
>                |          |          |          syscall_trace_enter
>                |          |          |          do_syscall_64
>                |          |          | return_from_SYSCALL_64
>                |          |          |          |
>                |          |          | --23.47%--epoll_pwait
> [...]

OK, this implicates the systemtap runtime utrace-emulation code that
looks for mmap/exec syscalls.  Perhaps there could be a mode (a -D
setting?)  for selecting kprobes rather than syscall-tracepoints to
catch those events.


- FChE