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authorNicolai Hähnle <Nicolai.Haehnle@amd.com>2016-12-21 19:46:40 +0100
committerIngo Molnar <mingo@kernel.org>2017-01-14 11:14:55 +0100
commit27bd57aa81d976211e1b2ddbc85bec06bddeb7e3 (patch)
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parent977625a693283dbb35b2a3f674bc0237f7347348 (diff)
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locking/ww_mutex/Documentation: Update the design document
Document the invariants we maintain for the wait list of ww_mutexes. Signed-off-by: Nicolai Hähnle <Nicolai.Haehnle@amd.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Chris Wilson <chris@chris-wilson.co.uk> Cc: Daniel Vetter <daniel@ffwll.ch> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Maarten Lankhorst <dev@mblankhorst.nl> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: dri-devel@lists.freedesktop.org Link: http://lkml.kernel.org/r/1482346000-9927-13-git-send-email-nhaehnle@gmail.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'Documentation/locking')
-rw-r--r--Documentation/locking/ww-mutex-design.txt12
1 files changed, 8 insertions, 4 deletions
diff --git a/Documentation/locking/ww-mutex-design.txt b/Documentation/locking/ww-mutex-design.txt
index 8a112dc304c3..34c3a1b50b9a 100644
--- a/Documentation/locking/ww-mutex-design.txt
+++ b/Documentation/locking/ww-mutex-design.txt
@@ -309,11 +309,15 @@ Design:
normal mutex locks, which are far more common. As such there is only a small
increase in code size if wait/wound mutexes are not used.
+ We maintain the following invariants for the wait list:
+ (1) Waiters with an acquire context are sorted by stamp order; waiters
+ without an acquire context are interspersed in FIFO order.
+ (2) Among waiters with contexts, only the first one can have other locks
+ acquired already (ctx->acquired > 0). Note that this waiter may come
+ after other waiters without contexts in the list.
+
In general, not much contention is expected. The locks are typically used to
- serialize access to resources for devices. The only way to make wakeups
- smarter would be at the cost of adding a field to struct mutex_waiter. This
- would add overhead to all cases where normal mutexes are used, and
- ww_mutexes are generally less performance sensitive.
+ serialize access to resources for devices.
Lockdep:
Special care has been taken to warn for as many cases of api abuse