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| author | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2013-12-11 22:59:09 +0100 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2013-12-16 11:36:15 +0100 |
| commit | 17eb88e068430014deb709e5af34197cdf2390c9 (patch) | |
| tree | 869d7c1e27ff7eeb2b0b846b8f844d32ac375222 /kernel/rcu | |
| parent | locking: Add an smp_mb__after_unlock_lock() for UNLOCK+BLOCK barrier (diff) | |
| download | linux-17eb88e068430014deb709e5af34197cdf2390c9.tar.xz linux-17eb88e068430014deb709e5af34197cdf2390c9.zip | |
Documentation/memory-barriers.txt: Downgrade UNLOCK+BLOCK
Historically, an UNLOCK+LOCK pair executed by one CPU, by one
task, or on a given lock variable has implied a full memory
barrier. In a recent LKML thread, the wisdom of this historical
approach was called into question:
http://www.spinics.net/lists/linux-mm/msg65653.html, in part due
to the memory-order complexities of low-handoff-overhead queued
locks on x86 systems.
This patch therefore removes this guarantee from the
documentation, and further documents how to restore it via a new
smp_mb__after_unlock_lock() primitive.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: <linux-arch@vger.kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/1386799151-2219-6-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/rcu')
0 files changed, 0 insertions, 0 deletions