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@xxxxxxxxxx> > Cc: Jonathan Corbet <corbet@xxxxxxx> > Cc: Gustavo Padovan <gustavo@xxxxxxxxxxx> > Cc: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx> > Cc: Sean Paul <seanpaul@xxxxxxxxxxxx> > Cc: David Airlie <airlied@xxxxxxxx> > Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx> > Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx> > Cc: Josh Triplett <josh@xxxxxxxxxxxxxxxx> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > Cc: Kate Stewart <kstewart@xxxxxxxxxxxxxxxxxxx> > Cc: Philippe Ombredanne <pombredanne@xxxxxxxx> > Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> > Cc: linux-doc@xxxxxxxxxxxxxxx > Cc: linux-media@xxxxxxxxxxxxxxx > Cc: linaro-mm-sig@xxxxxxxxxxxxxxxx > Co-authored-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx> > Signed-off-by: Thomas Hellstrom <thellstrom@xxxxxxxxxx> > > --- > 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@xxxxxxxxxxxxx>
