linux-kernel - Re: [TIP][RFC 2/7] futex: futex_top

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Date:	Mon, 09 Mar 2009 11:04:36 -0700
From:	Darren Hart <dvhltc@...ibm.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	"lkml, " <linux-kernel@...r.kernel.org>,
	Steven Rostedt <srostedt@...hat.com>,
	Sripathi Kodi <sripathik@...ibm.com>,
	John Stultz <johnstul@...ux.vnet.ibm.com>
Subject: Re: [TIP][RFC 2/7] futex: futex_top_waiter()

Thomas Gleixner wrote:
> On Mon, 2 Mar 2009, Darren Hart wrote:
> 
>> From: Darren Hart <dvhltc@...ibm.com>
>>
>> Improve legibility by wrapping finding the top waiter in a function.  This
>> will be used by the follow-on patches for enabling requeue pi.
>> +static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb,
>> +					union futex_key *key)
> 
> Can we just have *head as argument instead of *hb ?
> 
>> +{
>> +	struct plist_head *head;
>> +	struct futex_q *this;
>> +	struct futex_q *top_waiter = NULL;
> 
>   	struct futex_q *this;
> 
>> +	head = &hb->chain;
>> +	plist_for_each_entry(this, head, list) {
>> +		if (match_futex(&this->key, key)) {
>   		   	return this;		    
> 
>> +			top_waiter = this;
>> +			break;
>> +		}
>> +	}
>> +	return top_waiter;
> 
>   	return NULL;
> 
> Makes the function half the size.

I'd prefer to keep a futex_hash_bucket in the signature as a plist_head 
doesn't help describe what the function does.  However, I believe I have
addressed your concerns as to length with the following.  Does this look
acceptable?  I'll be resending the entire V6 patch series soon.

/**
  * futex_top_waiter - return the highest priority waiter on a futex
  * @hb:     the hash bucket the futex_q's reside in
  * @key:    the futex key (to distinguish it from other futex futex_q's)
  *
  * Must be called with the hb lock held.
  **/
static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb,
					union futex_key *key)
{
	struct futex_q *this;

	plist_for_each_entry(this, &hb->chain, list) {
		if (match_futex(&this->key, key))
			return this;
	}
	return NULL;
}



-- 
Darren Hart
IBM Linux Technology Center
Real-Time Linux Team
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