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[PATCH v2 10/11] Documentation/locking/ww_mutex: Update the design document

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From: Nicolai Hähnle <Nicolai.Haehnle@amd.com>

Document the invariants we maintain for the wait list of ww_mutexes.

Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Maarten Lankhorst <dev@mblankhorst.nl>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Nicolai Hähnle <Nicolai.Haehnle@amd.com>
---
 Documentation/locking/ww-mutex-design.txt | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/Documentation/locking/ww-mutex-design.txt b/Documentation/locking/ww-mutex-design.txt
index 8a112dc..34c3a1b 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
-- 
2.7.4

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[PATCH v2 00/11] locking/ww_mutex: Keep sorted wait list to avoid stampedes Nicolai Hähnle <nhaehnle@gmail.com> - 2016-12-01 15:10 +0100
  [PATCH v2 05/11] locking/ww_mutex: Add waiters in stamp order Nicolai Hähnle <nhaehnle@gmail.com> - 2016-12-01 15:10 +0100
    Re: [PATCH v2 05/11] locking/ww_mutex: Add waiters in stamp order Chris Wilson <chris@chris-wilson.co.uk> - 2016-12-01 17:10 +0100
    Re: [PATCH v2 05/11] locking/ww_mutex: Add waiters in stamp order Peter Zijlstra <peterz@infradead.org> - 2016-12-06 16:40 +0100
    Re: [PATCH v2 05/11] locking/ww_mutex: Add waiters in stamp order Peter Zijlstra <peterz@infradead.org> - 2016-12-06 18:00 +0100
  [PATCH v2 07/11] locking/ww_mutex: Wake at most one waiter for back off when acquiring the lock Nicolai Hähnle <nhaehnle@gmail.com> - 2016-12-01 15:10 +0100
  [PATCH v2 10/11] Documentation/locking/ww_mutex: Update the design document Nicolai Hähnle <nhaehnle@gmail.com> - 2016-12-01 15:10 +0100
  [PATCH v2 09/11] locking/mutex: Initialize mutex_waiter::ww_ctx with poison when debugging Nicolai Hähnle <nhaehnle@gmail.com> - 2016-12-01 15:10 +0100
  [PATCH v2 02/11] locking/ww_mutex: Re-check ww->ctx in the inner optimistic spin loop Nicolai Hähnle <nhaehnle@gmail.com> - 2016-12-01 15:10 +0100
    Re: [PATCH v2 02/11] locking/ww_mutex: Re-check ww->ctx in the inner  optimistic spin loop Chris Wilson <chris@chris-wilson.co.uk> - 2016-12-01 15:40 +0100
    Re: [PATCH v2 02/11] locking/ww_mutex: Re-check ww->ctx in the inner  optimistic spin loop Peter Zijlstra <peterz@infradead.org> - 2016-12-06 16:10 +0100
      Re: [PATCH v2 02/11] locking/ww_mutex: Re-check ww->ctx in the inner  optimistic spin loop Waiman Long <longman@redhat.com> - 2016-12-06 17:10 +0100
        Re: [PATCH v2 02/11] locking/ww_mutex: Re-check ww->ctx in the inner  optimistic spin loop Waiman Long <longman@redhat.com> - 2016-12-06 19:50 +0100
        Re: [PATCH v2 02/11] locking/ww_mutex: Re-check ww->ctx in the inner  optimistic spin loop Peter Zijlstra <peterz@infradead.org> - 2016-12-06 20:10 +0100
  [PATCH v2 01/11] drm/vgem: Use ww_mutex_(un)lock even with a NULL context Nicolai Hähnle <nhaehnle@gmail.com> - 2016-12-01 15:10 +0100
    Re: [PATCH v2 01/11] drm/vgem: Use ww_mutex_(un)lock even with a  NULL context Chris Wilson <chris@chris-wilson.co.uk> - 2016-12-01 15:20 +0100
      Re: [PATCH v2 01/11] drm/vgem: Use ww_mutex_(un)lock even with a  NULL context Daniel Vetter <daniel@ffwll.ch> - 2016-12-01 16:20 +0100
    Re: [PATCH v2 01/11] drm/vgem: Use ww_mutex_(un)lock even with a  NULL context Peter Zijlstra <peterz@infradead.org> - 2016-12-01 17:30 +0100
  [PATCH v2 11/11] [rfc] locking/ww_mutex: Always spin optimistically for the first waiter Nicolai Hähnle <nhaehnle@gmail.com> - 2016-12-01 15:10 +0100
  [PATCH v2 06/11] locking/ww_mutex: Notify waiters that have to back off while adding tasks to wait list Nicolai Hähnle <nhaehnle@gmail.com> - 2016-12-01 15:10 +0100

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