Message-ID: <53515232.50905@hp.com>
Date: Fri, 18 Apr 2014 12:26:26 -0400
From: Waiman Long <waiman.long@hp.com>
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To: Ingo Molnar <mingo@kernel.org>
CC: Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, linux-arch@vger.kernel.org,
        x86@kernel.org, linux-kernel@vger.kernel.org,
        virtualization@lists.linux-foundation.org,
        xen-devel@lists.xenproject.org, kvm@vger.kernel.org,
        Paolo Bonzini <paolo.bonzini@gmail.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Rik van Riel <riel@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>,
        David Vrabel <david.vrabel@citrix.com>,
        Oleg Nesterov <oleg@redhat.com>, Gleb Natapov <gleb@redhat.com>,
        Scott J Norton <scott.norton@hp.com>, Chegu Vinod <chegu_vinod@hp.com>
Subject: Re: [PATCH v9 05/19] qspinlock: Optimize for smaller NR_CPUS
References: <1397747051-15401-1-git-send-email-Waiman.Long@hp.com> <1397747051-15401-6-git-send-email-Waiman.Long@hp.com> <20140417155844.GS11096@twins.programming.kicks-ass.net> <53504C4E.8060800@hp.com> <20140418074616.GB13517@gmail.com>
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On 04/18/2014 03:46 AM, Ingo Molnar wrote:
> * Waiman Long<waiman.long@hp.com>  wrote:
>
>> On 04/17/2014 11:58 AM, Peter Zijlstra wrote:
>>> On Thu, Apr 17, 2014 at 11:03:57AM -0400, Waiman Long wrote:
>>>> +static __always_inline void
>>>> +clear_pending_set_locked(struct qspinlock *lock, u32 val)
>>>> +{
>>>> +	struct __qspinlock *l = (void *)lock;
>>>> +
>>>> +	ACCESS_ONCE(l->locked_pending) = 1;
>>>> +}
>>>> @@ -157,8 +251,13 @@ static inline int trylock_pending(struct qspinlock *lock, u32 *pval)
>>>>   	 * we're pending, wait for the owner to go away.
>>>>   	 *
>>>>   	 * *,1,1 ->   *,1,0
>>>> +	 *
>>>> +	 * this wait loop must be a load-acquire such that we match the
>>>> +	 * store-release that clears the locked bit and create lock
>>>> +	 * sequentiality; this because not all try_clear_pending_set_locked()
>>>> +	 * implementations imply full barriers.
>>> You renamed the function referred in the above comment.
>>>
>> Sorry, will fix the comments.
> I suggest not renaming the function instead.
> try_clear_pending_set_locked() tells the intent in a clearer fashion.
>
> Thanks,
>
> 	Ingo

I usually use the word "try" if there is a possibility of failure. 
However, the function will always succeed, albeit by waiting a bit in 
some cases. That is why I remove "try" from the name.

-Longman
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