From: Nicolai Hähnle <Nicolai.Haehnle@amd.com>
Date: Wed, 21 Dec 2016 18:46:40 +0000 (+0100)
Subject: locking/ww_mutex/Documentation: Update the design document
X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=27bd57aa81d976211e1b2ddbc85bec06bddeb7e3;p=GitHub%2FLineageOS%2Fandroid_kernel_motorola_exynos9610.git

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>
---

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