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Re: RFC: Always-on elision with per-process opt-in using tunables.
- From: "Tulio Magno Quites Machado Filho" <tuliom at linux dot vnet dot ibm dot com>
- To: "Carlos O'Donell" <carlos at redhat dot com>, GNU C Library <libc-alpha at sourceware dot org>
- Cc:
- Date: Mon, 15 May 2017 16:59:13 -0300
- Subject: Re: RFC: Always-on elision with per-process opt-in using tunables.
- Authentication-results: sourceware.org; auth=none
- References: <de358ecb-120d-a579-5998-cdbee930ba01@redhat.com>
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It could be useful, although it's outdated: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