Re: [PATCH bpf-next v1 2/5] cgroup: bpf: add cgroup_rstat_updated() and cgroup_rstat_flush() kfuncs

[Yosry Ahmed]

On Fri, May 20, 2022 at 4:16 AM Tejun Heo <tj@xxxxxxxxxx> wrote:
>
> On Fri, May 20, 2022 at 03:06:07PM +0530, Kumar Kartikeya Dwivedi wrote:
> > With static noinline, the compiler will optimize away the function. With global
> > noinline, it can still optimize away the call site, but will keep the function
> > definition, so attach works. Therefore __weak is needed to ensure call is still
> > emitted. With GCC __attribute__((noipa)) might have been more appropritate, but
> > LLVM doesn't support it, so __weak is the next best thing supported by both with
> > the same side effect.

Thanks a lot for the explanation!

>
> Ah, okay, so it's to prevent compiler from optimizing away call to a noop
> function by telling it that we don't know what the function might eventually
> be. Thanks for the explanation. Yosry, can you please add a comment
> explaining what's going on?

Will add a comment explaining things in the next section.  Thanks for
reviewing this, Tejun!

>
> Thanks.
>
> --
> tejun