From: Tony Luck <tony.luck@intel.com>
Date: Fri, 25 Sep 2009 15:42:16 +0000 (-0700)
Subject: [IA64] implement ticket locks for Itanium
X-Git-Tag: v2.6.32-rc1~8^2
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=2c86963b093c1a0887dfc6b32c6e5ea3a80f2922;p=pandora-kernel.git

[IA64] implement ticket locks for Itanium

Back in January 2008 Nick Piggin implemented "ticket" spinlocks
for X86 (See commit 314cdbefd1fd0a7acf3780e9628465b77ea6a836).

IA64 implementation has a couple of differences because of the
available atomic operations ... e.g. we have no fetchadd2 instruction
that operates on a 16-bit quantity so we make ticket locks use
a 32-bit word for each of the current ticket and now-serving values.

Performance on uncontended locks is about 8% worse than the previous
implementation, but this seems a good trade for determinism in the
contended case. Performance impact on macro-level benchmarks is in
the noise.

Signed-off-by: Tony Luck <tony.luck@intel.com>
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