From: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Date: Sun, 14 Mar 2010 19:33:51 +0000 (-0400)
Subject: urcu: Add extra "engineering safety factor" memory barrier in update_counter_and_wait()
X-Git-Tag: v0.4.4~7
X-Git-Url: http://git.liburcu.org/?a=commitdiff_plain;h=935b11ff4cf9053954d21b9d63c4ee367b12a652;hp=935b11ff4cf9053954d21b9d63c4ee367b12a652;p=userspace-rcu.git

urcu: Add extra "engineering safety factor" memory barrier in update_counter_and_wait()

Even though the memory barriers within update_counter_and_wait() are proven not
to be needed in urcu-mb/signal/qsbr implementations, we leave them in place as
an engineering safety factor. Basically, we've proven they are not required
(formally for urcu-mb and urcu-signal by model checking, less formally for
urcu-qsbr by looking at the execution order of concurrent synchronize_rcu() and
RCU read-sides with out-of-order load/stores). However, given that on the
overall performance impact of synchronize_rcu(), these memory barriers do not
add a significant overhead, let's leave them in place with a comment stating
that they are not required.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
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