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

[Bradley Morgan]

On 19 September 2026 18:00:06 BST, Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>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?
>

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