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Date: Wed, 12 Oct 2016 10:59:32 -0700
From: Davidlohr Bueso <dave@stgolabs.net>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Waiman Long <waiman.long@hpe.com>, Jason Low <jason.low2@hpe.com>,
        Ding Tianhong <dingtianhong@huawei.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Will Deacon <Will.Deacon@arm.com>, Ingo Molnar <mingo@redhat.com>,
        Imre Deak <imre.deak@intel.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Tim Chen <tim.c.chen@linux.intel.com>, Terry Rudd <terry.rudd@hpe.com>,
        "Paul E. McKenney" <paulmck@us.ibm.com>, Jason Low <jason.low2@hp.com>,
        Chris Wilson <chris@chris-wilson.co.uk>,
        Daniel Vetter <daniel.vetter@ffwll.ch>
Subject: Re: [PATCH -v4 2/8] locking/mutex: Rework mutex::owner
Message-ID: <20161012175932.GA4908@linux-80c1.suse>
References: <20161007145243.361481786@infradead.org>
 <20161007150210.995135898@infradead.org>
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On Fri, 07 Oct 2016, Peter Zijlstra wrote:
>+/*
>+ * Optimistic trylock that only works in the uncontended case. Make sure to
>+ * follow with a __mutex_trylock() before failing.
>+ */
>+static __always_inline bool __mutex_trylock_fast(struct mutex *lock)
>+{
>+	unsigned long curr = (unsigned long)current;
>+
>+	if (!atomic_long_cmpxchg_acquire(&lock->owner, 0UL, curr))
>+		return true;

Do we want to do a ccas check for !lock->owner? Although I can see a possible
case of 'optimizing for the contended' reasons for nay.

Thanks,
Davidlohr