linux-kernel - Re: [PATCH v6 1/6] locking/qspinlock: relaxes cmpxchg & xchg ops in native code

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Date:	Fri, 11 Sep 2015 15:27:44 -0700
From:	Davidlohr Bueso <dave@...olabs.net>
To:	Waiman Long <Waiman.Long@....com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org, Scott J Norton <scott.norton@...com>,
	Douglas Hatch <doug.hatch@...com>
Subject: Re: [PATCH v6 1/6] locking/qspinlock: relaxes cmpxchg & xchg ops in
 native code

On Fri, 11 Sep 2015, Waiman Long wrote:

>@@ -46,7 +46,7 @@ static inline bool virt_queued_spin_lock(struct qspinlock *lock)
> 	if (!static_cpu_has(X86_FEATURE_HYPERVISOR))
> 		return false;
>
>-	while (atomic_cmpxchg(&lock->val, 0, _Q_LOCKED_VAL) != 0)
>+	while (atomic_cmpxchg_acquire(&lock->val, 0, _Q_LOCKED_VAL) != 0)
> 		cpu_relax();

This code has changed with Peter's recent ccas fix. And the whole virt_queued_spin_lock()
thing will now be under pv configs. So this doesn't apply to native code anymore, so it
looks like it should be dropped altogether.

Thanks,
Davidlohr
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