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From: Waiman Long <waiman.long@hp.com>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>,
	Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>,
	kvm@vger.kernel.org, Peter Zijlstra <peterz@infradead.org>,
	virtualization@lists.linux-foundation.org,
	Andi Kleen <andi@firstfloor.org>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Michel Lespinasse <walken@google.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	linux-arch@vger.kernel.org, Gleb Natapov <gleb@redhat.com>,
	x86@kernel.org, Ingo Molnar <mingo@redhat.com>,
	xen-devel@lists.xenproject.org,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	Rik van Riel <riel@redhat.com>, Arnd Bergmann <arnd@arndb.de>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	Scott J Norton <scott.norton@hp.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Chris Wright <chrisw@sous-sol.org>,
	Alok Kataria <akataria@vmware.com>,
	Aswin Chandramouleeswaran <aswin@hp.com>,
	Chegu Vinod <chegu_vinod@hp.com>
Subject: Re: [PATCH v5 2/8] qspinlock, x86: Enable x86-64 to use queue spinlock
Date: Tue, 04 Mar 2014 10:06:07 -0500	[thread overview]
Message-ID: <5315EBDF.90304@hp.com> (raw)
In-Reply-To: <20140302141058.GA15629@redhat.com>

On 03/02/2014 09:10 AM, Oleg Nesterov wrote:
> On 02/26, Waiman Long wrote:
>> +#define _ARCH_SUPPORTS_ATOMIC_8_16_BITS_OPS
>> +
>> +/*
>> + * x86-64 specific queue spinlock union structure
>> + */
>> +union arch_qspinlock {
>> +	struct qspinlock slock;
>> +	u8		 lock;	/* Lock bit	*/
>> +};
> And this enables the optimized version of queue_spin_setlock().
>
> But why does it check ACCESS_ONCE(qlock->lock) == 0 ? This is called
> right after queue_get_lock_qcode() returns 0, this locked should be
> likely unlocked.
>
> Oleg.
>

Yes, the read check in queue_spin_setlock is probably redundant. Will 
remove that.

-Longman

WARNING: multiple messages have this Message-ID (diff)
From: Waiman Long <waiman.long@hp.com>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>,
	Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>,
	kvm@vger.kernel.org, Peter Zijlstra <peterz@infradead.org>,
	virtualization@lists.linux-foundation.org,
	Andi Kleen <andi@firstfloor.org>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Michel Lespinasse <walken@google.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	linux-arch@vger.kernel.org, Gleb Natapov <gleb@redhat.com>,
	x86@kernel.org, Ingo Molnar <mingo@redhat.com>,
	xen-devel@lists.xenproject.org,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	Rik van Riel <riel@redhat.com>, Arnd Bergmann <arnd@arndb.de>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	Scott J Norton <scott.norton@hp.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Chris Wright <chrisw@sous-sol.org>,
	Alok Kataria <akataria@vmware.com>,
	Aswin Chandramouleeswaran <aswin@hp.com>,
	Chegu Vinod <chegu_vinod@hp.com>, Boris Ostrovsky <
Subject: Re: [PATCH v5 2/8] qspinlock, x86: Enable x86-64 to use queue spinlock
Date: Tue, 04 Mar 2014 10:06:07 -0500	[thread overview]
Message-ID: <5315EBDF.90304@hp.com> (raw)
In-Reply-To: <20140302141058.GA15629@redhat.com>

On 03/02/2014 09:10 AM, Oleg Nesterov wrote:
> On 02/26, Waiman Long wrote:
>> +#define _ARCH_SUPPORTS_ATOMIC_8_16_BITS_OPS
>> +
>> +/*
>> + * x86-64 specific queue spinlock union structure
>> + */
>> +union arch_qspinlock {
>> +	struct qspinlock slock;
>> +	u8		 lock;	/* Lock bit	*/
>> +};
> And this enables the optimized version of queue_spin_setlock().
>
> But why does it check ACCESS_ONCE(qlock->lock) == 0 ? This is called
> right after queue_get_lock_qcode() returns 0, this locked should be
> likely unlocked.
>
> Oleg.
>

Yes, the read check in queue_spin_setlock is probably redundant. Will 
remove that.

-Longman

  reply	other threads:[~2014-03-04 15:06 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-02-27  4:32 [PATCH v5 0/8] qspinlock: a 4-byte queue spinlock with PV support Waiman Long
2014-02-27  4:32 ` [PATCH v5 1/8] qspinlock: Introducing a 4-byte queue spinlock implementation Waiman Long
2014-02-27  4:32 ` Waiman Long
2014-03-02 13:12   ` Oleg Nesterov
2014-03-02 13:12   ` Oleg Nesterov
2014-03-04 14:46     ` Waiman Long
2014-03-04 14:46     ` Waiman Long
2014-03-04 14:46       ` Waiman Long
2014-03-02 13:31   ` Oleg Nesterov
2014-03-02 13:31   ` Oleg Nesterov
2014-03-04 14:58     ` Waiman Long
2014-03-04 14:58     ` Waiman Long
2014-03-04 14:58       ` Waiman Long
2014-02-27  4:32 ` [PATCH v5 2/8] qspinlock, x86: Enable x86-64 to use queue spinlock Waiman Long
2014-03-02 14:10   ` Oleg Nesterov
2014-03-02 14:10   ` Oleg Nesterov
2014-03-04 15:06     ` Waiman Long [this message]
2014-03-04 15:06       ` Waiman Long
2014-03-04 15:06     ` Waiman Long
2014-02-27  4:32 ` Waiman Long
2014-02-27  4:32 ` [PATCH v5 3/8] qspinlock, x86: Add x86 specific optimization for 2 contending tasks Waiman Long
2014-02-27  4:32 ` Waiman Long
2014-03-02 13:16   ` Oleg Nesterov
2014-03-04 14:54     ` Waiman Long
2014-03-04 14:54       ` Waiman Long
2014-03-04 14:54     ` Waiman Long
2014-03-02 13:16   ` Oleg Nesterov
2014-02-27  4:32 ` [PATCH RFC v5 4/8] pvqspinlock, x86: Allow unfair spinlock in a real PV environment Waiman Long
2014-02-27  4:32 ` Waiman Long
2014-02-27  4:32 ` [PATCH RFC v5 5/8] pvqspinlock, x86: Enable unfair queue spinlock in a KVM guest Waiman Long
2014-02-27  4:32 ` Waiman Long
2014-02-27  4:32 ` [PATCH RFC v5 6/8] pvqspinlock, x86: Rename paravirt_ticketlocks_enabled Waiman Long
2014-02-27  4:32 ` Waiman Long
2014-02-27  4:32 ` [PATCH RFC v5 7/8] pvqspinlock, x86: Add qspinlock para-virtualization support Waiman Long
2014-02-27  4:32 ` Waiman Long
2014-02-27  4:32 ` [PATCH RFC v5 8/8] pvqspinlock, x86: Enable KVM to use qspinlock's PV support Waiman Long
2014-02-27  4:32 ` Waiman Long
2014-02-27  8:37 ` [PATCH v5 0/8] qspinlock: a 4-byte queue spinlock with " Peter Zijlstra
2014-02-27  8:37 ` Peter Zijlstra
2014-02-27  8:37   ` Peter Zijlstra
2014-02-27 18:25   ` Waiman Long
2014-02-27 18:25   ` Waiman Long
2014-02-27 18:25     ` Waiman Long
  -- strict thread matches above, loose matches on Subject: below --
2014-02-26 15:14 Waiman Long
2014-02-26 15:14 ` [PATCH v5 2/8] qspinlock, x86: Enable x86-64 to use queue spinlock Waiman Long
2014-02-26 15:14 ` Waiman Long

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