On Tue, Jun 19, 2018 at 10:24:44AM +0200, Thomas Hellstrom wrote:
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
Documentation/locking/ww-mutex-design.txt | 57 +++++++++-- drivers/dma-buf/reservation.c | 2 +- drivers/gpu/drm/drm_modeset_lock.c | 2 +- include/linux/ww_mutex.h | 17 ++- kernel/locking/locktorture.c | 2 +- kernel/locking/mutex.c | 165 +++++++++++++++++++++++++++--- kernel/locking/test-ww_mutex.c | 2 +- lib/locking-selftest.c | 2 +- 8 files changed, 213 insertions(+), 36 deletions(-)
Acked-by: Peter Zijlstra (Intel) peterz@infradead.org