linux-kernel - [PATCH RFC 0/2] locking: Fix ww_mutex algorithm inconsistency.

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Date:   Fri, 25 May 2018 14:38:53 +0200
From:   Thomas Hellstrom <thellstrom@...are.com>
To:     maarten.lankhosrt@...ux.intel.com, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH RFC 0/2] locking: Fix ww_mutex algorithm inconsistency.

The algorithm used for linux Wound/Wait mutexes, is actually not Wound/Wait
but Wait/Die. See for example

http://www.mathcs.emory.edu/~cheung/Courses/554/Syllabus/8-recv+serial/deadlock-compare.html

Rather than renaming them across the tree to something like Wait/Die mutexes or
Deadlock Avoidance mutexes, this patch set implements also the Wound/Wait
algorithm It shouldn't touch the binary ordinary mutex paths when compiled
with otpimization.
We use Wound/Wait for the modeset locks which in theory may benefit slightly
from Wound/Wait rather than Wait/Die, but Wait/Die is actually superior for
larger number of simultaneous contending transactions so we keep the original
implementation as a choice, and don't touch the algorithm used by the
reservation objects.

Performance- and functional testing has been done using 

git://people.freedesktop.org/~thomash/ww_mutex_test

Using WW_BUILTIN and 4 and 16 competing threads.

Another option is of course to ignore the the naming / algorithm inconsistency.