netdev - Re: [PATCH] netfilter: finer grained nf

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Message-ID: <49D9F086.7090905@trash.net>
Date:	Mon, 06 Apr 2009 14:07:34 +0200
From:	Patrick McHardy <kaber@...sh.net>
To:	Stephen Hemminger <shemminger@...tta.com>
CC:	Eric Dumazet <dada1@...mosbay.com>,
	David Miller <davem@...emloft.net>,
	Rick Jones <rick.jones2@...com>, netdev@...r.kernel.org,
	netfilter-devel@...r.kernel.org
Subject: Re: [PATCH] netfilter: finer grained nf_conn locking

Stephen Hemminger wrote:
> On Mon, 30 Mar 2009 21:57:15 +0200
> Eric Dumazet <dada1@...mosbay.com> wrote:
> 
>> On normal machines, (no debugging spinlocks), patch uses an embedded
>> spinlock. We probably can use this even on 32bit kernels, considering
>> previous patch removed the rcu_head (8 bytes on 32bit arches) from
>> nf_conn :)
>>
>> if LOCKDEP is on, size of a spinlock is 64 bytes on x86_64.
>> Adding a spinlock on each nf_conn would be too expensive. In this
>> case, an array of spinlock is a good compromise, as done in
>> IP route cache, tcp ehash, ...
>>
>> I agree sizing of this hash table is not pretty, and should be
>> a generic kernel service (I wanted such service for futexes for example)
>>
> 
> IMO having different locking based on lockdep and architecture is an invitation
> to future obscure problems. Perhaps some other locking method or shrinking
> ct entry would be better.

I agree. Do people enable lockdep on production machines? Otherwise
I'd say the size increase doesn't really matter.
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