1. 14 Apr, 2011 1 commit
  2. 14 Jan, 2009 1 commit
    • Peter Zijlstra's avatar
      mutex: implement adaptive spinning · 0d66bf6d
      Peter Zijlstra authored
      Change mutex contention behaviour such that it will sometimes busy wait on
      acquisition - moving its behaviour closer to that of spinlocks.
      
      This concept got ported to mainline from the -rt tree, where it was originally
      implemented for rtmutexes by Steven Rostedt, based on work by Gregory Haskins.
      
      Testing with Ingo's test-mutex application (http://lkml.org/lkml/2006/1/8/50)
      gave a 345% boost for VFS scalability on my testbox:
      
       # ./test-mutex-shm V 16 10 | grep "^avg ops"
       avg ops/sec:               296604
      
       # ./test-mutex-shm V 16 10 | grep "^avg ops"
       avg ops/sec:               85870
      
      The key criteria for the busy wait is that the lock owner has to be running on
      a (different) cpu. The idea is that as long as the owner is running, there is a
      fair chance it'll release the lock soon, and thus we'll be better off spinning
      instead of blocking/scheduling.
      
      Since regular mutexes (as opposed to rtmutexes) do not atomically track the
      owner, we add the owner in a non-atomic fashion and deal with the races in
      the slowpath.
      
      Furthermore, to ease the testing of the performance impact of this new code,
      there is means to disable this behaviour runtime (without having to reboot
      the system), when scheduler debugging is enabled (CONFIG_SCHED_DEBUG=y),
      by issuing the following command:
      
       # echo NO_OWNER_SPIN > /debug/sched_features
      
      This command re-enables spinning again (this is also the default):
      
       # echo OWNER_SPIN > /debug/sched_features
      Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
      Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
      0d66bf6d
  3. 03 Jul, 2006 3 commits
  4. 26 Jun, 2006 1 commit
  5. 09 Jan, 2006 1 commit