Re: [PATCH 01/28] hazptr: Implement Hazard Pointers

[Linus Torvalds]

On Sat, 19 Sept 2026 at 09:35, Bradley Morgan <brads@xxxxxxxxxxxxxx> wrote:
>
> I think hazard pointers are good, what test do YOU suggest we do here?

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".

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.

                  Linus