strace(1) is a wonderful command to trace system calls and signals, also known as profiling. The strace command comes stock with most, if not all, flavors of Linux

A typical incantation I use is

strace -tT -f -o /tmp/strace.out "<command + arguments>"

Examination of the resulting file /tmp/strace.out will often yield valuable clues to why a command is slow, where the slowdown is visible by gaps in the timed output.