netdev - Re: tun: Use netif_receive_skb instead of netif

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Message-ID: <20100519120547.GB26584@hmsreliant.think-freely.org>
Date:	Wed, 19 May 2010 08:05:47 -0400
From:	Neil Horman <nhorman@...hat.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Herbert Xu <herbert@...dor.hengli.com.au>,
	"David S. Miller" <davem@...emloft.net>,
	Thomas Graf <tgraf@...hat.com>, netdev@...r.kernel.org
Subject: Re: tun: Use netif_receive_skb instead of netif_rx

On Wed, May 19, 2010 at 10:18:09AM +0200, Eric Dumazet wrote:
> Le mercredi 19 mai 2010 à 10:09 +0200, Eric Dumazet a écrit :
> 
> > Another concern I have is about RPS.
> > 
> > netif_receive_skb() must be called from process_backlog() context, or
> > there is no guarantee the IPI will be sent if this skb is enqueued for
> > another cpu.
> 
> Hmm, I just checked again, and this is wrong.
> 
> In case we enqueue skb on a remote cpu backlog, we also
> do __raise_softirq_irqoff(NET_RX_SOFTIRQ); so the IPI will be done
> later.
> 
But if this happens, then we loose the connection between the packet being
received and the process doing the reception, so the network cgroup classifier
breaks again.

Performance gains are still a big advantage here of course.
Neil

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