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

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Message-ID: <1285397350.2478.102.camel@edumazet-laptop>
Date:	Sat, 25 Sep 2010 08:49:10 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Tom Herbert <therbert@...gle.com>
Cc:	netdev@...r.kernel.org, davem@...emloft.net, chavey@...gle.com
Subject: Re: [PATCH] net: reset skb queue mapping when rx'ing over tunnel

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>


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