Delays and puns

It's four per CPU; so on modern systems you can probably safely assume at least eight. That said, all that happens if you overflow the per-CPU slots is that they go on the linked list and cause a slight performance penalty. Whether that penalty is worse than contention on your mutexes is the kind of performance question that I think should probably be solved via measurement, and not via too much ungrounded speculation.

At a guess, though, I would expect contention on a mutex, which involves suspending tasks and performing context switches, to be much more expensive than scanning the hazard pointer list, at least until you get up to hundreds of concurrent entries.