linux-kernel - Re: [PATCH] netfilter: use per-cpu recursive lock (v11)

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Message-ID: <20090421092223.GA19049@ioremap.net>
Date:	Tue, 21 Apr 2009 13:22:23 +0400
From:	Evgeniy Polyakov <zbr@...emap.net>
To:	Eric Dumazet <dada1@...mosbay.com>
Cc:	Lai Jiangshan <laijs@...fujitsu.com>,
	Stephen Hemminger <shemminger@...tta.com>,
	Paul Mackerras <paulus@...ba.org>, paulmck@...ux.vnet.ibm.com,
	David Miller <davem@...emloft.net>, kaber@...sh.net,
	torvalds@...ux-foundation.org, jeff.chua.linux@...il.com,
	mingo@...e.hu, 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 (v11)

On Tue, Apr 21, 2009 at 10:55:59AM +0200, Eric Dumazet (dada1@...mosbay.com) wrote:
> Maybe just dont care about calling several time local_bh_disable()
> (since we were doing this in previous kernels anyway, we used to call read_lock_bh())
> 
> This shortens fastpath, is faster than local_irq_save()/local_irq_restore(),
> and looks better.

Yeah, given that non-nested locking is more likely condition, it will be
even faster than preemption case.

> void xt_info_rdlock_bh(void)
> {
> 	struct xt_info_lock *lock;
> 
> 	local_bh_disable();
>  	lock = &__get_cpu_var(xt_info_locks);
>  	if (likely(++lock->depth == 0))
>  		spin_lock(&lock->lock);
> }
> 
> void xt_info_rdunlock_bh(void)
> {
> 	struct xt_info_lock *lock = &__get_cpu_var(xt_info_locks);
> 
> 	BUG_ON(lock->depth < 0);
> 	if (likely(--lock->depth < 0))
> 		 spin_unlock(&lock->lock);
> 	local_bh_enable();
> }
> 
> 

-- 
	Evgeniy Polyakov
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