netdev - Re: [PATCH net-next RFC v2] switchdev: bridge: drop hardware forwarded packets

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Message-ID: <20150324175825.GA1465@roeck-us.net>
Date:	Tue, 24 Mar 2015 10:58:25 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	roopa <roopa@...ulusnetworks.com>
Cc:	Jiri Pirko <jiri@...nulli.us>, Scott Feldman <sfeldma@...il.com>,
	John Fastabend <john.fastabend@...il.com>,
	Andrew Lunn <andrew@...n.ch>,
	David Miller <davem@...emloft.net>,
	"Arad, Ronen" <ronen.arad@...el.com>,
	Netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next RFC v2] switchdev: bridge: drop hardware
 forwarded packets

On Tue, Mar 24, 2015 at 10:45:03AM -0700, roopa wrote:
> On 3/24/15, 9:01 AM, Guenter Roeck wrote:
> >On Tue, Mar 24, 2015 at 03:29:21PM +0100, Jiri Pirko wrote:
> >>>diff --git a/drivers/net/ethernet/rocker/rocker.c
> >>>b/drivers/net/ethernet/rocker/rocker.c
> >>>index aab962c..0f7217f7 100644
> >>>--- a/drivers/net/ethernet/rocker/rocker.c
> >>>+++ b/drivers/net/ethernet/rocker/rocker.c
> >>>@@ -3931,15 +3931,28 @@ unmap_frag:
> >>>        return -EMSGSIZE;
> >>>}
> >>>
> >>>+static bool rocker_port_dev_check(struct net_device *dev);
> >>>+
> >>>static netdev_tx_t rocker_port_xmit(struct sk_buff *skb, struct
> >>>net_device *dev)
> >>>{
> >>>        struct rocker_port *rocker_port = netdev_priv(dev);
> >>>        struct rocker *rocker = rocker_port->rocker;
> >>>        struct rocker_desc_info *desc_info;
> >>>        struct rocker_tlv *frags;
> >>>+       struct net_device *in_dev;
> >>>        int i;
> >>>        int err;
> >>>
> >>>+       if (rocker_port_is_bridged(rocker_port)) {
> >>>+               rcu_read_lock();
> >>>+               in_dev = dev_get_by_index_rcu(dev_net(dev), skb->skb_iif);
> >>Hmm, you iterate over all ports for every xmit call :/
> >>Would be nicer if skb_iif would be netdev poiter. Not sure it is doable.
> >>
> >It may be easier (and faster) to loop through all rocker ports and try to find
> >one with the same ifindex. Then the dev_check call would not be necessary.
> >
> This is still overhead for every packet on the switches we support. The
> number of ports can go close to 128
> (40G ports can be broken into 4x10G ports).
> 
Agreed. Given that, and since dev_get_by_index_rcu uses a hash to find the
device pointer, it may actually be (much) faster (and the above "iterate
over all ports" is a bit misleading).

I tested the above approach with DSA and a Marvell switch chip. It works,
but I am a bit concerned about the per-packet overhead, especially
in larger networks. I would prefer if there would be a means to 'catch'
duplicate packets earlier - before they are even created, if that is
possible.

Guenter
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