[Bug 1560634] [NEW] [Ubuntu 16.04.1] Provide a way to dynamically enable lock elision on glibc

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We identified that, in some scenarios, lock elision can cause performance regressions.
In order to minimize this, we prepared a patch for POWER that disables lock elision by default even when glibc is built with --enable-lock-elision.
It's enabled only when GLIBC_ELISION_ENABLE=yes is available in the environment and when the hardware supports it.

This patch has already been sent upstream [1], but the community asked us to re-implement it based on the tunables framework.  It's now blocked waiting for the acceptance of the tunables framework [2] [3] [4].  The discussion around the tunables framework is already old and the community cannot agree yet on a way to pass the tuning parameters.
We had an agreement it would be integrated into glibc 2.23, which didn't happen and due to other issues, we don't believe this will happen until glibc 2.24.

Meanwhile, in order to solve the regression issues reported by current customers, would you consider to accept the following patch?
It's very close to patch [1], which has already been refused upstream.

[1] http://patchwork.sourceware.org/patch/8529/
[2] http://patchwork.sourceware.org/patch/10405/
[3] http://patchwork.sourceware.org/patch/10405/
[4] http://patchwork.sourceware.org/patch/10342/

** Affects: glibc (Ubuntu)
     Importance: Medium
     Assignee: Adam Conrad (adconrad)
         Status: Triaged


** Tags: architecture-ppc64le bugnameltc-139420 severity-medium targetmilestone-inin16041
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[Ubuntu 16.04.1] Provide a way to dynamically enable lock elision on glibc
https://bugs.launchpad.net/bugs/1560634
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