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Date:	Sun, 20 Apr 2014 18:20:02 -0400 (EDT)
From:	David Miller <>
Subject: Re: [PATCH 2/2] macvlan: Move broadcasts into a work queue

From: Herbert Xu <>
Date: Thu, 17 Apr 2014 13:45:59 +0800

> Currently broadcasts are handled in network RX context, where
> the packets are sent through netif_rx.  This means that the number
> of macvlans will be constrained by the capacity of netif_rx.
> For example, setting up 4096 macvlans practically causes all
> broadcast packets to be dropped as the default netif_rx queue
> size simply can't handle 4096 skbs being stuffed into it all
> at once.
> Fundamentally, we need to ensure that the amount of work handled
> in each netif_rx backlog run is constrained.  As broadcasts are
> anything but constrained, it either needs to be limited per run
> or moved to process context.
> This patch picks the second option and moves all broadcast handling
> bar the trivial case of packets going to a single interface into
> a work queue.  Obviously there also needs to be a limit on how
> many broadcast packets we postpone in this way.  I've arbitrarily
> chosen tx_queue_len of the master device as the limit (act_mirred
> also happens to use this parameter in a similar way).
> In order to ensure we don't exceed the backlog queue we will use
> netif_rx_ni instead of netif_rx for broadcast packets.
> Signed-off-by: Herbert Xu <>

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