Clicking through his links to various posts about e.g. stack pointers or flame graphs, my takeaway is he's an outlier in productivity, and got a lot done in 3.5 years at a monstrously large organization.
I'm pretty envious of his capabilities, in 3.5 years I can ship a couple webapps, I would never personally get JVM compilation flags added.
Conversely, I made HotSpot commits as an intern, but I never shipped a web app.
Brendan Gregg is somewhat of a systems engineering legend and contributed more to the field than most people could dream of.
Is his post self promotion? Yeah, probably.
Does it matter and do the top 3 comments on HN be salty about that? Probably not that useful.