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Re: sem_lock() vs qspinlocks

From Peter Zijlstra <peterz@infradead.org>
Newsgroups linux.kernel
Subject Re: sem_lock() vs qspinlocks
Date 2016-05-20 23:00 +0200
Message-ID <rAZGy-2cl-3@gated-at.bofh.it> (permalink)
References <rALkd-1uD-9@gated-at.bofh.it> <rANvH-2Kb-1@gated-at.bofh.it> <rAUdP-74l-5@gated-at.bofh.it> <rAZwS-27c-15@gated-at.bofh.it>
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On Fri, May 20, 2016 at 04:47:43PM -0400, Waiman Long wrote:

> >Similarly, and I know you hate it, but afaict, then semantically
> >queued_spin_is_contended() ought to be:
> >
> >-       return atomic_read(&lock->val) & ~_Q_LOCKED_MASK;
> >+       return atomic_read(&lock->val);
> >

> Looking for contended lock, you need to consider the lock waiters also. So
> looking at the whole word is right.

No, you _only_ need to look at the lock waiters.

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Thread

sem_lock() vs qspinlocks Davidlohr Bueso <dave@stgolabs.net> - 2016-05-20 07:40 +0200
  Re: sem_lock() vs qspinlocks Peter Zijlstra <peterz@infradead.org> - 2016-05-20 10:00 +0200
    Re: sem_lock() vs qspinlocks Davidlohr Bueso <dave@stgolabs.net> - 2016-05-20 17:10 +0200
      Re: sem_lock() vs qspinlocks Peter Zijlstra <peterz@infradead.org> - 2016-05-20 17:10 +0200
        Re: sem_lock() vs qspinlocks Davidlohr Bueso <dave@stgolabs.net> - 2016-05-20 17:30 +0200
        Re: sem_lock() vs qspinlocks Peter Zijlstra <peterz@infradead.org> - 2016-05-20 17:30 +0200
      Re: sem_lock() vs qspinlocks Waiman Long <waiman.long@hpe.com> - 2016-05-20 22:50 +0200
        Re: sem_lock() vs qspinlocks Peter Zijlstra <peterz@infradead.org> - 2016-05-20 23:00 +0200
          Re: sem_lock() vs qspinlocks Davidlohr Bueso <dave@stgolabs.net> - 2016-05-21 03:00 +0200
            Re: sem_lock() vs qspinlocks Waiman Long <waiman.long@hpe.com> - 2016-05-21 06:10 +0200
              Re: sem_lock() vs qspinlocks Peter Zijlstra <peterz@infradead.org> - 2016-05-21 09:50 +0200
  Re: sem_lock() vs qspinlocks Peter Zijlstra <peterz@infradead.org> - 2016-05-20 10:00 +0200
  Re: sem_lock() vs qspinlocks Peter Zijlstra <peterz@infradead.org> - 2016-05-20 10:20 +0200
    Re: sem_lock() vs qspinlocks Peter Zijlstra <peterz@infradead.org> - 2016-05-20 10:20 +0200
      Re: sem_lock() vs qspinlocks Peter Zijlstra <peterz@infradead.org> - 2016-05-20 11:40 +0200
  Re: sem_lock() vs qspinlocks Peter Zijlstra <peterz@infradead.org> - 2016-05-20 10:40 +0200
    Re: sem_lock() vs qspinlocks Peter Zijlstra <peterz@infradead.org> - 2016-05-20 11:10 +0200
      Re: sem_lock() vs qspinlocks Ingo Molnar <mingo@kernel.org> - 2016-05-20 12:10 +0200
        Re: sem_lock() vs qspinlocks Mel Gorman <mgorman@techsingularity.net> - 2016-05-20 12:50 +0200
  Re: sem_lock() vs qspinlocks Peter Zijlstra <peterz@infradead.org> - 2016-05-20 14:00 +0200
    Re: sem_lock() vs qspinlocks Boqun Feng <boqun.feng@gmail.com> - 2016-05-20 16:10 +0200
      Re: sem_lock() vs qspinlocks Peter Zijlstra <peterz@infradead.org> - 2016-05-20 17:30 +0200
        Re: sem_lock() vs qspinlocks Peter Zijlstra <peterz@infradead.org> - 2016-05-20 18:10 +0200
          Re: sem_lock() vs qspinlocks Linus Torvalds <torvalds@linux-foundation.org> - 2016-05-20 19:10 +0200
            Re: sem_lock() vs qspinlocks Peter Zijlstra <peterz@infradead.org> - 2016-05-20 23:10 +0200
              Re: sem_lock() vs qspinlocks Linus Torvalds <torvalds@linux-foundation.org> - 2016-05-20 23:50 +0200
                Re: sem_lock() vs qspinlocks Davidlohr Bueso <dave@stgolabs.net> - 2016-05-21 02:50 +0200
                Re: sem_lock() vs qspinlocks Linus Torvalds <torvalds@linux-foundation.org> - 2016-05-21 04:40 +0200
                Re: sem_lock() vs qspinlocks Peter Zijlstra <peterz@infradead.org> - 2016-05-21 09:40 +0200
                Re: sem_lock() vs qspinlocks Manfred Spraul <manfred@colorfullife.com> - 2016-05-21 15:50 +0200
                Re: sem_lock() vs qspinlocks Peter Zijlstra <peterz@infradead.org> - 2016-05-24 13:00 +0200
                Re: sem_lock() vs qspinlocks Davidlohr Bueso <dave@stgolabs.net> - 2016-05-21 19:20 +0200
            Re: sem_lock() vs qspinlocks Peter Zijlstra <peterz@infradead.org> - 2016-05-23 14:30 +0200
              Re: sem_lock() vs qspinlocks Linus Torvalds <torvalds@linux-foundation.org> - 2016-05-23 20:00 +0200
                Re: sem_lock() vs qspinlocks Boqun Feng <boqun.feng@gmail.com> - 2016-05-25 08:40 +0200
          Re: sem_lock() vs qspinlocks Manfred Spraul <manfred@colorfullife.com> - 2016-05-22 10:50 +0200
            Re: sem_lock() vs qspinlocks Peter Zijlstra <peterz@infradead.org> - 2016-05-22 11:40 +0200
    Re: sem_lock() vs qspinlocks Davidlohr Bueso <dave@stgolabs.net> - 2016-05-20 18:30 +0200
    Re: sem_lock() vs qspinlocks Waiman Long <waiman.long@hpe.com> - 2016-05-20 22:50 +0200
      Re: sem_lock() vs qspinlocks Peter Zijlstra <peterz@infradead.org> - 2016-05-20 23:00 +0200

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