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[Bug 1556096] [NEW] [Ubuntu 16.04.1] RELEASE and ACQUIRE atomics on Power


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Will Deacon proposed the RELEASE/ACQUIRE/RELAXED semantics for atomic
operations(https://lkml.org/lkml/2015/8/6/498), which has been already
merged in 4.3-rc1. More people tend to use it for better
performance(https://lkml.org/lkml/2015/9/20/47). These semantics are
proposed for better fitting the need of high scalability.

 However, the efficient implementation hasn't been merged yet. As we
have a weaker memory order model on POWER, if we didn't implement these
atomics efficently, there would be no benefit we can gain from these new

A proposal of an efficient implemenation has been sent out to
upstream(https://lkml.org/lkml/2015/9/16/527), hopefully will get
merged. Still there may be more atomics having RELEASE and ACQUIRE
semantics, and there need more effort to implement them correctly. Also,
we need to spread these new atomic variants to LTC kernel team to
understand what they can provide and how to use them.

> Was this feature already accepted upstream?

Not yet, still waiting to get into the maintainer's tree, but there is
no obvious objection to this feature.

** Affects: linux (Ubuntu)
     Importance: Medium
     Assignee: Canonical Kernel Team (canonical-kernel-team)
         Status: Incomplete

** Tags: architecture-ppc64le bot-comment bugnameltc-136580 severity-medium targetmilestone-inin16041
[Ubuntu 16.04.1] RELEASE and ACQUIRE atomics on Power
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