netdev - Re: [PATCH net-next-2.6] net: Xmit Packet Steering (XPS)

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Message-ID: <4B071654.6040300@gmail.com>
Date:	Fri, 20 Nov 2009 23:21:08 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jarek Poplawski <jarkao2@...il.com>
CC:	"David S. Miller" <davem@...emloft.net>,
	Tom Herbert <therbert@...gle.com>,
	Linux Netdev List <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next-2.6] net: Xmit Packet Steering (XPS)

Jarek Poplawski a écrit :
> On Fri, Nov 20, 2009 at 10:43:55PM +0100, Eric Dumazet wrote:
>>> Hmm... Actually, why did I have to do lockdep's job...
>> In fact I could not find why irq masking is necessary, and lockdep is
>> fine with my code and my testings. Care to explain what problem you spotted ?
>>
> 
> CPU1						 CPU2
> net_rx_action()					 net_rx_action()
>  xps_flush()				  	  xps_flush()
>   q = &per_cpu(xps_pcpu_queue, cpu2)		   q = &per_cpu(xps_pcpu_queue, cpu1)
>   spin_lock(&q->list.lock of cpu2)		   spin_lock(&q->list.lock of cpu1)
> 
> <IPI>						 <IPI>
> remote_free_skb_list()				 remote_free_skb_list()
> waiting on spin_lock(&q->list.lock of cpu1)	 waiting on spin_lock(&q->list.lock of cpu2)
> 
> 
> IPIs triggerered e.g. by CPU3 (or/and CPU4...) doing net_rx_action as well.
> 

:) Now I am convinced :)

Thanks jarek


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