netdev - Re: [PATCH] net: reset skb queue mapping when rx'ing over tunnel

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Message-Id: <20100926.184856.229756077.davem@davemloft.net>
Date:	Sun, 26 Sep 2010 18:48:56 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	therbert@...gle.com, netdev@...r.kernel.org, chavey@...gle.com
Subject: Re: [PATCH] net: reset skb queue mapping when rx'ing over tunnel

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Sat, 25 Sep 2010 08:49:10 +0200

> Le vendredi 24 septembre 2010 à 09:18 -0700, Tom Herbert a écrit :
>> > Hmm...
>> >
>> > This would need to be reverted later when tunnels are updated to be
>> > multiqueue aware ? I made an attempt with GRE some days ago.
>> >
>> > I dont understand why this patch is needed, since get_rps_cpu() has a
>> > check anyway
>> >
>> I think the skb queue_mapping should correspond to a queue in the
>> skb's device as an invariant.  In the case that an skb's device is
>> change from a multiqueue device to single queue device (like GRE), the
>> inconsistency in the queue_mapping is fairly innocuous, we get one
>> warning but will pretty much take the unlikely branch for GRE packets
>> then on.  But imagine a case where skb's device was change from one
>> multiqueue device to another, but the queue mapping was not also
>> updated.  This  would cause poor weighting in get_rps_cpus.  For
>> example, if the new device had fewer queues than the old one,
>> get_rps_cpu will bias toward using queue 0's rps mask.
> 
> I believe your patch is fine. Thanks
> 
> Acked-by: Eric Dumazet <eric.dumazet@...il.com>

Applied, thanks everyone.
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