I've been following Brendan since the Sun Microsystems days with his Dtrace book which opened my eyes to the world of system call tracing from user-space to kernel. Linux at the time had a hodgepodge of tracing utilities (SystemTap, Ktap etc..) that usually required kernel modules to work properly. Strace was my goto in Linux back then but slowed down the target binary a lot. Thank the universe for eBPF and Brendan's current books that today we have powerful tracing capabilities in Linux that rivals Dtrace in FreeBSD/Illumos. If you want to understand the internals of an operating system and how things work, without being a kernel developer, systems performance engineering is a way to go.