]> git.proxmox.com Git - mirror_ubuntu-eoan-kernel.git/commit
locking: Implement an algorithm choice for Wound-Wait mutexes
authorThomas Hellstrom <thellstrom@vmware.com>
Fri, 15 Jun 2018 08:17:38 +0000 (10:17 +0200)
committerThomas Hellstrom <thellstrom@vmware.com>
Tue, 3 Jul 2018 07:44:36 +0000 (09:44 +0200)
commit08295b3b5beec9aac0f7a9db86f0fc3792039da3
tree6226474d5fdaba0bf04aa8bf6542a89722547990
parent55f036ca7e74b85e34958af3d22121c656796413
locking: Implement an algorithm choice for Wound-Wait mutexes

The current Wound-Wait mutex algorithm is actually not Wound-Wait but
Wait-Die. Implement also Wound-Wait as a per-ww-class choice. Wound-Wait
is, contrary to Wait-Die a preemptive algorithm and is known to generate
fewer backoffs. Testing reveals that this is true if the
number of simultaneous contending transactions is small.
As the number of simultaneous contending threads increases, Wait-Wound
becomes inferior to Wait-Die in terms of elapsed time.
Possibly due to the larger number of held locks of sleeping transactions.

Update documentation and callers.

Timings using git://people.freedesktop.org/~thomash/ww_mutex_test
tag patch-18-06-15

Each thread runs 100000 batches of lock / unlock 800 ww mutexes randomly
chosen out of 100000. Four core Intel x86_64:

Algorithm    #threads       Rollbacks  time
Wound-Wait   4              ~100       ~17s.
Wait-Die     4              ~150000    ~19s.
Wound-Wait   16             ~360000    ~109s.
Wait-Die     16             ~450000    ~82s.

Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Gustavo Padovan <gustavo@padovan.org>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Sean Paul <seanpaul@chromium.org>
Cc: David Airlie <airlied@linux.ie>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Kate Stewart <kstewart@linuxfoundation.org>
Cc: Philippe Ombredanne <pombredanne@nexb.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-doc@vger.kernel.org
Cc: linux-media@vger.kernel.org
Cc: linaro-mm-sig@lists.linaro.org
Co-authored-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Ingo Molnar <mingo@kernel.org>
Documentation/locking/ww-mutex-design.txt
drivers/dma-buf/reservation.c
drivers/gpu/drm/drm_modeset_lock.c
include/linux/ww_mutex.h
kernel/locking/locktorture.c
kernel/locking/mutex.c
kernel/locking/test-ww_mutex.c
lib/locking-selftest.c