From: roopa <roopa@cumulusnetworks•com>
To: sfeldma@gmail•com
Cc: netdev@vger•kernel.org, jiri@resnulli•us,
simon.horman@netronome•com, ronen.arad@intel•com,
john.r.fastabend@intel•com, andrew@lunn•ch, f.fainelli@gmail•com,
linux@roeck-us•net, davidch@broadcom•com,
stephen@networkplumber•org
Subject: Re: [RFC PATCH net-next 0/4] switchdev: avoid duplicate packet forwarding
Date: Mon, 15 Jun 2015 07:23:45 -0700 [thread overview]
Message-ID: <557EDFF1.3040109@cumulusnetworks.com> (raw)
In-Reply-To: <1434218670-43821-1-git-send-email-sfeldma@gmail.com>
On 6/13/15, 11:04 AM, sfeldma@gmail•com wrote:
> From: Scott Feldman <sfeldma@gmail•com>
>
> (RFC because we're at rc7+ now)
>
> With switchdev support for offloading L2/L3 forwarding data path to a
> switch device, we have a general problem where both the device and the
> kernel may forward the packet, resulting in duplicate packets on the wire.
> Anytime a packet is forwarded by the device and a copy is sent to the CPU,
> there is potential for duplicate forwarding, as the kernel may also do a
> forwarding lookup and send the packet on the wire.
>
> The specific problem this patch series is interested in solving is avoiding
> duplicate packets on bridged ports. There was a previous RFC from Roopa
> (http://marc.info/?l=linux-netdev&m=142687073314252&w=2) to address this
> problem, but didn't solve the problem of mixed ports in the bridge from
> different devices; there was no way to exclude some ports from forwarding
> and include others. This RFC solves that problem by tagging the ingressing
> packet with a unique mark, and then comparing the packet mark with the
> egress port mark, and skip forwarding when there is a match. For the mixed
> ports bridge case, only those ports with matching marks are skipped.
>
> The switchdev port driver must do two things:
>
> 1) Generate a fwd_mark for each switch port, using some unique key of the
> switch device (and optionally port). This is a one-time operation done
> when port's netdev is setup.
>
> 2) On packet ingress from port, mark the skb with the ingress port's
> fwd_mark. If the device supports it, it's useful to only mark skbs
> which were already forwarded by the device. If the device does not
> support such indication, all skbs can be marked, even if they're
> local dst.
>
> Two new 32-bit fields are added to struct sk_buff and struct netdevice to
> hold the fwd_mark. I've wrapped these with CONFIG_NET_SWITCHDEV for now. I
> tried using skb->mark for this purpose, but ebtables can overwrite the
> skb->mark before the bridge gets it, so that will not work.
>
> In general, this fwd_mark can be used for any case where a packet is
> forwarded by the device and a copy is sent to the CPU, to avoid the kernel
> re-forwarding the packet. sFlow is another use-case that comes to mind,
> but I haven't explored the details.
>
>
Acked-by: Roopa Prabhu <roopa@cumulusnetworks•com>
next prev parent reply other threads:[~2015-06-15 14:23 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-13 18:04 [RFC PATCH net-next 0/4] switchdev: avoid duplicate packet forwarding sfeldma
2015-06-13 18:04 ` [RFC PATCH net-next 1/4] net: don't reforward packets already forwarded by offload device sfeldma
2015-06-14 6:51 ` Jiri Pirko
2015-06-15 14:21 ` roopa
2015-06-13 18:04 ` [RFC PATCH net-next 2/4] switchdev: add fwd_mark generator helper sfeldma
2015-06-14 6:56 ` Jiri Pirko
2015-06-14 17:50 ` Scott Feldman
2015-06-15 5:46 ` Jiri Pirko
2015-06-15 13:52 ` Scott Feldman
2015-06-15 14:09 ` Sergei Shtylyov
2015-06-15 15:17 ` roopa
2015-06-13 18:04 ` [RFC PATCH net-next 3/4] rocker: add fwd_mark support sfeldma
2015-06-14 7:02 ` Jiri Pirko
2015-06-14 18:00 ` Scott Feldman
2015-06-15 5:49 ` Jiri Pirko
2015-06-13 18:04 ` [RFC PATCH net-next 4/4] switchdev: update documentation for fwd_mark sfeldma
2015-06-15 13:54 ` [RFC PATCH net-next 0/4] switchdev: avoid duplicate packet forwarding roopa
2015-06-15 14:23 ` roopa [this message]
2015-06-15 23:25 ` David Miller
2015-06-16 6:04 ` Jiri Pirko
2015-06-16 16:47 ` Scott Feldman
2015-06-16 21:11 ` Jiri Pirko
2015-06-16 23:53 ` Scott Feldman
2015-06-17 6:30 ` Jiri Pirko
2015-06-17 7:02 ` Scott Feldman
2015-06-17 10:23 ` Jamal Hadi Salim
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