linux-kernel - Re: [PATCH] netfilter: use per-CPU recursive lock {XIV}

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Date:	Fri, 24 Apr 2009 17:33:00 +0200
From:	Patrick McHardy <kaber@...sh.net>
To:	Eric Dumazet <dada1@...mosbay.com>
CC:	Stephen Hemminger <shemminger@...tta.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, Paul Mackerras <paulus@...ba.org>,
	paulmck@...ux.vnet.ibm.com, Evgeniy Polyakov <zbr@...emap.net>,
	David Miller <davem@...emloft.net>, jeff.chua.linux@...il.com,
	laijs@...fujitsu.com, jengelh@...ozas.de, r000n@...0n.net,
	linux-kernel@...r.kernel.org, netfilter-devel@...r.kernel.org,
	netdev@...r.kernel.org, benh@...nel.crashing.org,
	mathieu.desnoyers@...ymtl.ca
Subject: Re: [PATCH]  netfilter: use per-CPU recursive lock {XIV}

Eric Dumazet wrote:
> Stephen Hemminger a écrit :
>> In days of old in 2.6.29, netfilter did locketh using a 
>> lock of the reader kind when doing its table business, and do
>> a writer when with pen in hand like a overworked accountant
>> did replace the tables. This sucketh and caused the single
>> lock to fly back and forth like a poor errant boy.
>>
>> But then netfilter was blessed with RCU and the performance
>> was divine, but alas there were those that suffered for
>> trying to replace their many rules one at a time.
>>
>> So now RCU must be vanquished from the scene, and better
>> chastity belts be placed upon this valuable asset most dear.
>> The locks that were but one are now replaced by one per suitor.
>>
>> The repair was made after much discussion involving
>> Eric the wise, and Linus the foul. With flowers springing
>> up amid the thorns some peace has finally prevailed and
>> all is soothed. This patch and purple prose was penned by
>> in honor of "Talk like Shakespeare" day.

Hehe.

>>  static int __init xt_init(void)
>>  {
>> -	int i, rv;
>> +	unsigned int i;
>> +	int rv;
>> +	static struct lock_class_key xt_lock_key[NR_CPUS];
> 
> Could we avoid this [NR_CPUS] thing ?
> 
>> +
>> +	for_each_possible_cpu(i) {
>> +		rwlock_t *lock = &per_cpu(xt_info_locks, i);
>> +
>> +		rwlock_init(lock);
>> +		lockdep_set_class(lock, xt_lock_key+i);
>> +	}
> 
> 
> Did you tried :
> 
> static DECLARE_PER_CPU(struct lock_class_key, xt_locks_key);

Either way is fine with me, I'll wait for Stephen to state his opinion.
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