From: Nicolas Dichtel <nicolas.dichtel@6wind.com>
To: Ido Schimmel <idosch@mellanox.com>
Cc: Jiri Pirko <jiri@resnulli.us>,
Nikolay Aleksandrov <nikolay@cumulusnetworks.com>,
Roopa Prabhu <roopa@cumulusnetworks.com>,
netdev <netdev@vger.kernel.org>
Subject: Re: switchdev offload & ecmp
Date: Tue, 16 May 2017 22:22:02 +0200 [thread overview]
Message-ID: <eb9e0c4a-5862-d109-3272-38430b69f707@6wind.com> (raw)
In-Reply-To: <20170516141149.GA1874@splinter.mtl.com>
Le 16/05/2017 à 16:11, Ido Schimmel a écrit :
> On Tue, May 16, 2017 at 02:57:47PM +0200, Nicolas Dichtel wrote:
>>>> I suspect that there can be scenarii where some packets of a flow are forwarded
>>>> by the driver and some other are forwarded by the kernel.
>>>
>>> Can you elaborate? The kernel only sees specific packets, which were
>>> trapped to the CPU. See:
>>> https://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next.git/tree/drivers/net/ethernet/mellanox/mlxsw/spectrum.c#n2996
>> Ok, this part was not clear for me, thank you for the pointer.
>>
>> So, when an arp resolution is needed, the packets are not trapped to the CPU,
>> the device manages the queue itself?
>
> There are two cases here. If you need an ARP resolution following a hit
> of a directly connected route and this neighbour isn't in the device's
> table, then packet is trapped (HOST_MISS_IPV4 in above list) to the CPU
> and triggers ARP resolution in the kernel. Eventually a NETEVENT will be
> sent and the neighbour will be programmed to the device.
>
> If you need an ARP resolution of a nexthop, then this is a bit
> different. If you have an ECMP group with several nexthops, then once
> one of them is resolved, packets will be forwarded using it. To make
> sure other nexthops will also be resolved we try to periodically refresh
> them. Otherwise packets will always be forwarded using a single nexthop,
> as the kernel won't have motivation to resolve the others.
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c#n987
>
> In case no nexthops can be resolved, then packets will be trapped to the
> CPU (RTR_INGRESS0 in above list) and forwarded by the kernel.
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c#n1896
>
Ok, thank you for the details.
Regards,
Nicolas
prev parent reply other threads:[~2017-05-16 20:22 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-15 14:25 switchdev offload & ecmp Nicolas Dichtel
2017-05-15 16:40 ` Ido Schimmel
2017-05-16 12:57 ` Nicolas Dichtel
2017-05-16 14:11 ` Ido Schimmel
2017-05-16 20:22 ` Nicolas Dichtel [this message]
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