On 19 September 2026 18:00:06 BST, Linus Torvalds <[email protected]> wrote: >On Sat, 19 Sept 2026 at 09:35, Bradley Morgan <[email protected]> >wrote: >> >> I think hazard pointers are good, what test do YOU suggest we do here? >
Whew! Talking to my idol, best day ever. >I want to see a single real-world example of "look, this speeds this >real load up by 10%, and the kernel code was actually cleaned up in >the process because hazard pointers are great". well they are, but the big maintainer blokes would want to test and stuff. I'm just a measly reviewer. > >Not a microbenchmark that tests just the hazard pointers themselves, >but a real kernel feature that has been converted to hazard pointers, >and in the process actually shows improvement. > >The ONLY reason for hazard pointers to ever be merged is if they >actually buy us something real. > >So I want to see that 'real" thing. > >I want to see how easy/hard it is to actually convert a real current >user, and I want to see how it actually results in measurable >improvements in performance. > >Something *core*. Something that everybody uses. Because I'm not in >the least interested in a new subtle feature that interacts with the >scheduler and is only used for some random driver or (to pick the only >example I have ever seen) AppArmor. > >Now, obviously, the thing that would impress me is something like the >dcache. If *that* can be converted, and it shows real improvements on >some real benchmark, then I'm sold. > >Now, I don't really expect that kind of major test-case, but I do >expect *something* meaningful. Not a driver. Not a test module. Real >code. > >IOW: "Show me the money". > >Because the kernel is *not* some kind of acadmic project. Never has been. > >I simply don't want to merge something that is touted as an >alterantive to RCU - which we obviously depend on very very heavily - >without something *major* that actually uses it and shows the >real-world advantages. > >The discussion about hazard pointers in the kernel has been around for >a few years by now. If there isn't some real core feature that was >converted to show that, then I think that's already a failure >indication. > >I'm hoping that those patches and numbers already exist, and I just >haven't seen them. I hope this ends up being merged. > > Linus > --- Thanks! "I'm not a very positive person" - Linus torvalds
