netdev - Re: [PATCH net-next] net: better IFF_XMIT_DST

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Message-Id: <20141004.202900.1107815015981261576.davem@davemloft.net>
Date:	Sat, 04 Oct 2014 20:29:00 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH net-next] net: better IFF_XMIT_DST_RELEASE support

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Thu, 02 Oct 2014 09:34:07 -0700

> From: Eric Dumazet <edumazet@...gle.com>
> 
> Testing xmit_more support with netperf and connected UDP sockets,
> I found strange dst refcount false sharing.
> 
> Current handling of IFF_XMIT_DST_RELEASE is not optimal.
> 
> dropping dst in validate_xmit_skb() is certainly too late in case
> packet was queued by cpu X but dequeued by cpu Y
> 
> The logical point to take care of drop/force is in __dev_queue_xmit()
> before even taking qdisc lock.
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

I assume you are going to rework this to use a counter indication
in order to deal with the packet scheduler issues Julian brought
up.
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