netdev - Re: [PATCH] bridge: avoid ptype

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Date:	Wed, 28 Feb 2007 19:56:11 -0800
From:	Stephen Hemminger <shemminger@...ux-foundation.org>
To:	Ben Greear <greearb@...delatech.com>
Cc:	David Miller <davem@...emloft.net>, bridge@...ux-foundation.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH] bridge: avoid ptype_all packet handling

On Wed, 28 Feb 2007 17:28:09 -0800
Ben Greear <greearb@...delatech.com> wrote:

> Stephen Hemminger wrote:
> > I was measuring bridging/routing performance and noticed this.
> > 
> > The current code runs the "all packet" type handlers before calling
> > the bridge hook.  If an application (like some DHCP clients) is
> > using AF_PACKET, this means that each received packet gets run
> > through the Berkeley Packet Filter code in sk_run_filter (slow).
> > 
> > By moving the bridging hook to run first, the packets flowing
> > through the bridge get filtered out there. This results in a 14%
> > improvement in performance, but it does mean that some snooping
> > applications would miss packets if being used on a bridge.  The
> > correct way to see all packets on a bridge is to set the bridge
> > pseudo-device to promiscuous mode.
> 
> Seems it would be better to fix these clients to be more selective as
> to where they bind.

The problem is any use of BPF is a lose, if it has to be done to all
traffic.

> This breaks the case where you want to see packets on a particular
> interface, not just the entire bridge, right?

It might be possible to use promisc counter to handle this.
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