Systemtap caching behavior

[Mark Wielaard]

On Sun, Jan 13, 2019 at 09:58:39AM -0500, Mikhail Zhukovskiy wrote:
> One more, perhaps naive question. What I am trying to do is generate fame graphs per http://brendangregg.com/FlameGraphs/cpuflamegraphs.html . At the moment, I have succeeded in making the flame graphs in which the call stacks begin with entry_SYSCALL_64_fastpath. If I wanted to include the user space calls that made these system calls, would my next step be to re-compile the application that we are profiling (the BIND DNS daemon) with one of the gcc debug flags (https://gcc.gnu.org/onlinedocs/gcc/Debugging-Options.html)?

For just backtraces in user space on amd64 you shouldn't need to rebuild
userspace, since amd64 includes unwind tables by default. So backtraces
done from user space probes should work as is. But if you are unwinding
from kernel space into user space you might need the kernel debuginfo
installed (since the kernel normally doesn't include unwind tables,
so the will need to come from the .debug_frame).

Cheers,

Mark