RFC: Always-on elision with per-process opt-in using tunables.

[Tulio Magno Quites Machado Filho]

Carlos O'Donell <carlos@redhat.com> writes:

> I am going to propose the following:
>
> * Always build with elision support.
>
> * Elision disabled by default at runtime.
>
> * Use tunables to allow processes to opt-in to transparent elision.
>
> The benefit is that the elision support doesn't bit-rot, and we keep
> it working, and that distributions can conservatively backport elision
> and allow users to test enablement on a per-process basis.
>
> The elision is enabled with:
>
> GLIBC_TUNABLE=glibc.elision.enable=1

I like this proposal.

> The obvious set of patches are:
>
> (a) Split out some cleanups in this patch.
> (b) Always build with elision and us tunables to opt-in.
> (c) Extend tunables to allow modification of elision parameters
>     (useful for upcoming rwlock elision re-enablement).

Paul Murphy had a patch to implement this step.
It could be useful, although it's outdated:
https://patchwork.sourceware.org/patch/10342/

Another patch to the set you suggested:

 (d) Extend the testsuite to test elided locks too.

-- 
Tulio Magno