From: Michael Ellerman <mpe@ellerman.id.au>
Date: Wed, 15 Jan 2014 07:14:28 +0000 (+1100)
Subject: powerpc: Add support for the optimised lockref implementation
X-Git-Tag: v3.14-rc1~80^2~1
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=3405d230b374b6923878b21b8d708d7db1f734ef;p=pandora-kernel.git

powerpc: Add support for the optimised lockref implementation

This commit adds the architecture support required to enable the
optimised implementation of lockrefs.

That's as simple as defining arch_spin_value_unlocked() and selecting
the Kconfig option.

We also define cmpxchg64_relaxed(), because the lockref code does not
need the cmpxchg to have barrier semantics.

Using Linus' test case[1] on one system I see a 4x improvement for the
basic enablement, and a further 1.3x for cmpxchg64_relaxed(), for a
total of 5.3x vs the baseline.

On another system I see more like 2x improvement.

[1]: http://marc.info/?l=linux-fsdevel&m=137782380714721&w=4

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
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