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Date: Fri, 20 May 2016 22:52:22 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Waiman Long <waiman.long@hpe.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>, manfred@colorfullife.com,
        mingo@kernel.org, torvalds@linux-foundation.org, ggherdovich@suse.com,
        mgorman@techsingularity.net, linux-kernel@vger.kernel.org
Subject: Re: sem_lock() vs qspinlocks
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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.