True, there are scenarios when you might prefer to spin, but they're pretty specialized.
My blog post was quite clear that I'm talking about futexes
No, you never mention the word "futex."
When somebody says "mutex", you have to assume they already mean "futex".
I don't think that's a valid generalization at all.
What systems have mutexes that aren't built like futexes?
Especially given he was complaining about syscall costs . . . which are nonexistent with futexes . . .
At any rate, you've definitely overstated the case against mutexes in this post. At most, the advice should have been "avoid designs that will suffer from a lot of contention" like locking with lots of shared mutable state. It really has nothing to do with threads-vs-processes as you've made it out to do.
Correct. man 7 pthreads states:
In NPTL, thread synchronization primitives (mutexes, thread joining, and so on) are implemented using the Linux futex(2) system call.
A futex is a mutex that only does a system call if there is contention; you can google it.