perf - Perf is a simple app monitoring solution paired with meaningful alerts.
Valgrind - Valgrind is an instrumentation framework for building dynamic analysis tools.
ftrace - A function tracer for the Linux kernel.
strace - Trace system calls and signals. A diagnostic, debugging and instructional userspace utility.
DTrace - DTrace is a performance analysis and troubleshooting tool for Solaris, Mac OS X and FreeBSD.
SystemTap - SystemTap provides instrumentation for a live running kernel and user-space applications.