netdev - Re: tun: Use netif_receive_skb instead of netif

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Date:	Wed, 19 May 2010 18:20:47 +1000
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Thomas Graf <tgraf@...hat.com>,
	Neil Horman <nhorman@...hat.com>, netdev@...r.kernel.org
Subject: Re: tun: Use netif_receive_skb instead of netif_rx

On Wed, May 19, 2010 at 10:09:42AM +0200, Eric Dumazet wrote:
> 
> 6) netif_rx() pro is that packet processing is done while stack usage is
> guaranteed to be low (from process_backlog, using a special softirq
> stack, instead of current stack)
> 
> After your patch, tun will use more stack. Is it safe on all contexts ?

Dave also raised this but I believe nothing changes with regards
to the stack.  We currently call do_softirq which does not switch
stacks.

Only a real interrupt would switch stacks.

> 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.

Can you explain this a bit more?

Thanks,
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