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authorThomas Hellstrom <thellstrom@vmware.com>2018-06-15 11:17:38 +0300
committerThomas Hellstrom <thellstrom@vmware.com>2018-07-03 10:44:36 +0300
commit08295b3b5beec9aac0f7a9db86f0fc3792039da3 (patch)
tree6226474d5fdaba0bf04aa8bf6542a89722547990 /drivers/dma-buf/reservation.c
parent55f036ca7e74b85e34958af3d22121c656796413 (diff)
downloadlinux-08295b3b5beec9aac0f7a9db86f0fc3792039da3.tar.xz
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>
Diffstat (limited to 'drivers/dma-buf/reservation.c')
-rw-r--r--drivers/dma-buf/reservation.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/drivers/dma-buf/reservation.c b/drivers/dma-buf/reservation.c
index 314eb1071cce..20bf90f4ee63 100644
--- a/drivers/dma-buf/reservation.c
+++ b/drivers/dma-buf/reservation.c
@@ -46,7 +46,7 @@
* write-side updates.
*/
-DEFINE_WW_CLASS(reservation_ww_class);
+DEFINE_WD_CLASS(reservation_ww_class);
EXPORT_SYMBOL(reservation_ww_class);
struct lock_class_key reservation_seqcount_class;