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From: Davidlohr Bueso <dave@stgolabs.net>
To: Boqun Feng <boqun.feng@gmail.com>
Cc: Waiman Long <Waiman.Long@hpe.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	x86@kernel.org, linux-kernel@vger.kernel.org,
	Scott J Norton <scott.norton@hpe.com>,
	Douglas Hatch <doug.hatch@hpe.com>
Subject: Re: [PATCH tip/locking/core v8 1/5] locking/qspinlock: Use _acquire/_release versions of cmpxchg & xchg
Date: Mon, 19 Oct 2015 20:46:02 -0700	[thread overview]
Message-ID: <20151020034602.GC27292@linux-uzut.site> (raw)
In-Reply-To: <20151020031714.GA935@fixme-laptop.cn.ibm.com>

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On Tue, 20 Oct 2015, Boqun Feng wrote:

>> @@ -93,7 +94,7 @@ static __always_inline void queued_spin_unlock(struct qspinlock *lock)
>>  	/*
>>  	 * smp_mb__before_atomic() in order to guarantee release semantics
>>  	 */
>> -	smp_mb__before_atomic_dec();
>> +	smp_mb__before_atomic();
>>  	atomic_sub(_Q_LOCKED_VAL, &lock->val);
>
>Just be curious, you don't use atomic_sub_release() here on purpose?

atomic_sub() does not imply barriers, so there's no relaxed variants; that's
only for _return() (and such) to the caller.

Thanks,
Davidlohr

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  reply	other threads:[~2015-10-20  3:46 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-10-15 22:51 [PATCH tip/locking/core v8 0/5] locking/qspinlock: Enhance pvqspinlock performance Waiman Long
2015-10-15 22:51 ` [PATCH tip/locking/core v8 1/5] locking/qspinlock: Use _acquire/_release versions of cmpxchg & xchg Waiman Long
2015-10-20  3:17   ` Boqun Feng
2015-10-20  3:46     ` Davidlohr Bueso [this message]
2015-10-20  3:48       ` Boqun Feng
2015-10-15 22:51 ` [PATCH tip/locking/core v8 2/5] locking/pvqspinlock, x86: Optimize PV unlock code path Waiman Long
2015-10-15 22:51 ` [PATCH tip/locking/core v8 3/5] locking/pvqspinlock: Collect slowpath lock statistics Waiman Long
2015-10-15 22:51 ` [PATCH tip/locking/core v8 4/5] locking/pvqspinlock: Allow 1 lock stealing attempt Waiman Long
2015-10-15 22:51 ` [PATCH tip/locking/core v8 5/5] locking/pvqspinlock: Queue node adaptive spinning Waiman Long

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