Message-ID: <9d58f6dc-3508-6c10-d5ba-71b768ad2432@nvidia.com>
Date:   Mon, 6 Feb 2023 19:14:24 +0200
From:   Paul Blakey <paulb@...dia.com>
To:     Ilya Maximets <i.maximets@....org>, netdev@...r.kernel.org,
        Saeed Mahameed <saeedm@...dia.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        "David S. Miller" <davem@...emloft.net>
Cc:     Oz Shlomo <ozsh@...dia.com>, Jiri Pirko <jiri@...dia.com>,
        Roi Dayan <roid@...dia.com>, Vlad Buslov <vladbu@...dia.com>,
        Marcelo Leitner <mleitner@...hat.com>
Subject: Re: [PATCH net-next v8 0/7] net/sched: cls_api: Support hardware miss
 to tc action



On 06/02/2023 14:34, Ilya Maximets wrote:
> On 2/5/23 16:49, Paul Blakey wrote:
>> Hi,
>>
>> This series adds support for hardware miss to instruct tc to continue execution
>> in a specific tc action instance on a filter's action list. The mlx5 driver patch
>> (besides the refactors) shows its usage instead of using just chain restore.
>>
>> Currently a filter's action list must be executed all together or
>> not at all as driver are only able to tell tc to continue executing from a
>> specific tc chain, and not a specific filter/action.
>>
>> This is troublesome with regards to action CT, where new connections should
>> be sent to software (via tc chain restore), and established connections can
>> be handled in hardware.
>>
>> Checking for new connections is done when executing the ct action in hardware
>> (by checking the packet's tuple against known established tuples).
>> But if there is a packet modification (pedit) action before action CT and the
>> checked tuple is a new connection, hardware will need to revert the previous
>> packet modifications before sending it back to software so it can
>> re-match the same tc filter in software and re-execute its CT action.
>>
>> The following is an example configuration of stateless nat
>> on mlx5 driver that isn't supported before this patchet:
>>
>>   #Setup corrosponding mlx5 VFs in namespaces
>>   $ ip netns add ns0
>>   $ ip netns add ns1
>>   $ ip link set dev enp8s0f0v0 netns ns0
>>   $ ip netns exec ns0 ifconfig enp8s0f0v0 1.1.1.1/24 up
>>   $ ip link set dev enp8s0f0v1 netns ns1
>>   $ ip netns exec ns1 ifconfig enp8s0f0v1 1.1.1.2/24 up
>>
>>   #Setup tc arp and ct rules on mxl5 VF representors
>>   $ tc qdisc add dev enp8s0f0_0 ingress
>>   $ tc qdisc add dev enp8s0f0_1 ingress
>>   $ ifconfig enp8s0f0_0 up
>>   $ ifconfig enp8s0f0_1 up
>>
>>   #Original side
>>   $ tc filter add dev enp8s0f0_0 ingress chain 0 proto ip flower \
>>      ct_state -trk ip_proto tcp dst_port 8888 \
>>        action pedit ex munge tcp dport set 5001 pipe \
>>        action csum ip tcp pipe \
>>        action ct pipe \
>>        action goto chain 1
>>   $ tc filter add dev enp8s0f0_0 ingress chain 1 proto ip flower \
>>      ct_state +trk+est \
>>        action mirred egress redirect dev enp8s0f0_1
>>   $ tc filter add dev enp8s0f0_0 ingress chain 1 proto ip flower \
>>      ct_state +trk+new \
>>        action ct commit pipe \
>>        action mirred egress redirect dev enp8s0f0_1
>>   $ tc filter add dev enp8s0f0_0 ingress chain 0 proto arp flower \
>>        action mirred egress redirect dev enp8s0f0_1
>>
>>   #Reply side
>>   $ tc filter add dev enp8s0f0_1 ingress chain 0 proto arp flower \
>>        action mirred egress redirect dev enp8s0f0_0
>>   $ tc filter add dev enp8s0f0_1 ingress chain 0 proto ip flower \
>>      ct_state -trk ip_proto tcp \
>>        action ct pipe \
>>        action pedit ex munge tcp sport set 8888 pipe \
>>        action csum ip tcp pipe \
>>        action mirred egress redirect dev enp8s0f0_0
>>
>>   #Run traffic
>>   $ ip netns exec ns1 iperf -s -p 5001&
>>   $ sleep 2 #wait for iperf to fully open
>>   $ ip netns exec ns0 iperf -c 1.1.1.2 -p 8888
>>
>>   #dump tc filter stats on enp8s0f0_0 chain 0 rule and see hardware packets:
>>   $ tc -s filter show dev enp8s0f0_0 ingress chain 0 proto ip | grep "hardware.*pkt"
>>          Sent hardware 9310116832 bytes 6149672 pkt
>>          Sent hardware 9310116832 bytes 6149672 pkt
>>          Sent hardware 9310116832 bytes 6149672 pkt
>>
>> A new connection executing the first filter in hardware will first rewrite
>> the dst port to the new port, and then the ct action is executed,
>> because this is a new connection, hardware will need to be send this back
>> to software, on chain 0, to execute the first filter again in software.
>> The dst port needs to be reverted otherwise it won't re-match the old
>> dst port in the first filter. Because of that, currently mlx5 driver will
>> reject offloading the above action ct rule.
>>
>> This series adds supports partial offload of a filter's action list,
>> and letting tc software continue processing in the specific action instance
>> where hardware left off (in the above case after the "action pedit ex munge tcp
>> dport... of the first rule") allowing support for scenarios such as the above.
> 
> 
> Hi, Paul.  Not sure if this was discussed before, but don't we also need
> a new TCA_CLS_FLAGS_IN_HW_PARTIAL flag or something like this?
> 
> Currently the in_hw/not_in_hw flags are reported per filter, i.e. these
> flags are not per-action.  This may cause confusion among users, if flows
> are reported as in_hw, while they are actually partially or even mostly
> processed in SW.
> 
> What do you think?
> 
> Best regards, Ilya Maximets.

I think its a good idea, and I'm fine with proposing something like this 
in a different series, as this isn't a new problem from this series and 
existed before it, at least with CT rules.

So how about I'll propose it in a different series and we continue with 
this first?

Thanks,
Paul.

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