Re: [PATCH net-next v9 0/7] net/sched: cls_api: Support hardware miss to tc action

From: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
To: Paul Blakey <paulb@nvidia.com>
Cc: netdev@vger.kernel.org, Saeed Mahameed <saeedm@nvidia.com>,
	Paolo Abeni <pabeni@redhat.com>, Jakub Kicinski <kuba@kernel.org>,
	Eric Dumazet <edumazet@google.com>,
	Jamal Hadi Salim <jhs@mojatatu.com>,
	Cong Wang <xiyou.wangcong@gmail.com>,
	"David S. Miller" <davem@davemloft.net>,
	Oz Shlomo <ozsh@nvidia.com>, Jiri Pirko <jiri@nvidia.com>,
	Roi Dayan <roid@nvidia.com>, Vlad Buslov <vladbu@nvidia.com>
Subject: Re: [PATCH net-next v9 0/7] net/sched: cls_api: Support hardware miss to tc action
Date: Thu, 9 Feb 2023 17:56:07 -0800	[thread overview]
Message-ID: <20230210015607.xjq2gorwpg4q3zxv@t14s.localdomain> (raw)
In-Reply-To: <20230206174403.32733-1-paulb@nvidia.com>

Hi,

On Mon, Feb 06, 2023 at 07:43:56PM +0200, 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

I see Jamal had asked about stats on the other version, but then no
dependency was set. I think we _must_ have a dependency of this
patchet on the per-action stats one. Otherwise the stats above will
get messy.  Without the per-action stats, the last one is replicated
to the other actions. But then, will hw count the packet that it did
only the first action? I don't see how it would, and then for the all
but first one the packet will be accounted twice.

With this said, it would be nice to provide a sample of how the sw and
hw stats would look like _after_ this patchset as well.

Btw I'll add my Reviewed-by tag to the per-action stats one in a few.

> 
> 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,

We should avoid this terminology as is, as it can create confusion. It
is not that it is offloading action 1 and not action 2. Instead, it is
adding support to a more fine grained miss to sw. Perhaps "support for
partially executing in hw".

> 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.
> 
> Changelog:
> 	v1->v2:
> 	Fixed compilation without CONFIG_NET_CLS
> 	Cover letter re-write
> 
> 	v2->v3:
> 	Unlock spin_lock on error in cls flower filter handle refactor
> 	Cover letter
> 
> 	v3->v4:
> 	Silence warning by clang
> 
> 	v4->v5:
> 	Cover letter example
> 	Removed ifdef as much as possible by using inline stubs
> 
> 	v5->v6:
> 	Removed new inlines in cls_api.c (bot complained in patchwork)
> 	Added reviewed-by/ack - Thanks!
> 
> 	v6->v7:
> 	Removed WARN_ON from pkt path (leon)
> 	Removed unnecessary return in void func
> 
> 	v7->v8:
> 	Removed #if IS_ENABLED on skb ext adding Kconfig changes
> 	Complex variable init in seperate lines
> 	if,else if, else if ---> switch case
> 
> 	v8->v9:
> 	Removed even more IS_ENABLED because of Kconfig
> 
> Paul Blakey (7):
>   net/sched: cls_api: Support hardware miss to tc action
>   net/sched: flower: Move filter handle initialization earlier
>   net/sched: flower: Support hardware miss to tc action
>   net/mlx5: Kconfig: Make tc offload depend on tc skb extension
>   net/mlx5: Refactor tc miss handling to a single function
>   net/mlx5e: Rename CHAIN_TO_REG to MAPPED_OBJ_TO_REG
>   net/mlx5e: TC, Set CT miss to the specific ct action instance
> 
>  .../net/ethernet/mellanox/mlx5/core/Kconfig   |   4 +-
>  .../ethernet/mellanox/mlx5/core/en/rep/tc.c   | 225 ++------------
>  .../mellanox/mlx5/core/en/tc/sample.c         |   2 +-
>  .../ethernet/mellanox/mlx5/core/en/tc_ct.c    |  39 +--
>  .../ethernet/mellanox/mlx5/core/en/tc_ct.h    |   2 +
>  .../net/ethernet/mellanox/mlx5/core/en_rx.c   |   4 +-
>  .../net/ethernet/mellanox/mlx5/core/en_tc.c   | 280 ++++++++++++++++--
>  .../net/ethernet/mellanox/mlx5/core/en_tc.h   |  23 +-
>  .../net/ethernet/mellanox/mlx5/core/eswitch.h |   2 +
>  .../mellanox/mlx5/core/lib/fs_chains.c        |  14 +-
>  include/linux/skbuff.h                        |   6 +-
>  include/net/flow_offload.h                    |   1 +
>  include/net/pkt_cls.h                         |  34 ++-
>  include/net/sch_generic.h                     |   2 +
>  net/openvswitch/flow.c                        |   3 +-
>  net/sched/act_api.c                           |   2 +-
>  net/sched/cls_api.c                           | 213 ++++++++++++-
>  net/sched/cls_flower.c                        |  73 +++--
>  18 files changed, 602 insertions(+), 327 deletions(-)
> 
> -- 
> 2.30.1
> 