netdev - Re: [PATCH] netfilter: use per-cpu recursive lock (v10)

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Message-ID: <20090420215827.GK6822@linux.vnet.ibm.com>
Date:	Mon, 20 Apr 2009 14:58:27 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Paul Mackerras <paulus@...ba.org>
Cc:	Eric Dumazet <dada1@...mosbay.com>,
	Stephen Hemminger <shemminger@...tta.com>,
	Evgeniy Polyakov <zbr@...emap.net>,
	David Miller <davem@...emloft.net>, kaber@...sh.net,
	torvalds@...ux-foundation.org, jeff.chua.linux@...il.com,
	mingo@...e.hu, 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 (v10)

On Tue, Apr 21, 2009 at 07:23:31AM +1000, Paul Mackerras wrote:
> Eric Dumazet writes:
> 
> > OK, but we still have a problem on machines with >= 250 cpus,
> > because calling 250 times spin_lock() is going to overflow preempt_count,
> > as each spin_lock() increases preempt_count by one.
> 
> Huh?  Each cpu has its own separate preempt_count.

But a single CPU is acquiring one lock per CPU, so all the increments
are to one CPU's preempt_count.  :-(

							Thanx, Paul
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