From: Mikulas Patocka <mpatocka@redhat.com>
Date: Mon, 22 Oct 2012 23:37:47 +0000 (-0400)
Subject: percpu-rw-semaphores: use light/heavy barriers
X-Git-Tag: v3.7-rc3~6
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=5c1eabe68501d1e1b1586c7f4c46cc531828c4ab;p=pandora-kernel.git

percpu-rw-semaphores: use light/heavy barriers

This patch introduces new barrier pair light_mb() and heavy_mb() for
percpu rw semaphores.

This patch fixes a bug in percpu-rw-semaphores where a barrier was
missing in percpu_up_write.

This patch improves performance on the read path of
percpu-rw-semaphores: on non-x86 cpus, there was a smp_mb() in
percpu_up_read. This patch changes it to a compiler barrier and removes
the "#if defined(X86) ..." condition.

From: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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