netdev - Re: [net-next PATCH v3 7/8] net: ixgbe: add support for tc

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Date:	Wed, 17 Feb 2016 06:17:26 -0500
From:	Jamal Hadi Salim <jhs@...atatu.com>
To:	John Fastabend <john.fastabend@...il.com>, jiri@...nulli.us,
	amir@...ai.me, davem@...emloft.net
Cc:	netdev@...r.kernel.org, jeffrey.t.kirsher@...el.com
Subject: Re: [net-next PATCH v3 7/8] net: ixgbe: add support for tc_u32
 offload

On 16-02-17 12:18 AM, John Fastabend wrote:
> This adds initial support for offloading the u32 tc classifier. This
> initial implementation only implements a few base matches and actions
> to illustrate the use of the infrastructure patches.
>
> However it is an interesting subset because it handles the u32 next
> hdr logic to correctly map tcp packets from ip headers using the ihl
> and protocol fields. After this is accepted we can extend the match
> and action fields easily by updating the model header file.
>
> Also only the drop action is supported initially.
>
> Here is a short test script,
>
>   #tc qdisc add dev eth4 ingress
>   #tc filter add dev eth4 parent ffff: protocol ip \
> 	u32 ht 800: order 1 \
> 	match ip dst 15.0.0.1/32 match ip src 15.0.0.2/32 action drop
>

Note: i dont see anything that says "hw". Are you delegating ht 0x800
for h/w only? It is the default ht; so may not be the best choice.

> <-- hardware has dst/src ip match rule installed -->
>
>   #tc filter del dev eth4 parent ffff: prio 49152

Would be useful to dump the installed rule so user gets to
see kernel-assigned prio 49152. The better way
to do this is use the handle 800::1 as opposed to prio.

>   #tc filter add dev eth4 parent ffff: protocol ip prio 99 \
> 	handle 1: u32 divisor 1
>   #tc filter add dev eth4 protocol ip parent ffff: prio 99 \
> 	u32 ht 800: order 1 link 1: \
> 	offset at 0 mask 0f00 shift 6 plus 0 eat match ip protocol 6 ff
>   #tc filter add dev eth4 parent ffff: protocol ip \
> 	u32 ht 1: order 3 match tcp src 23 ffff action drop
>
> <-- hardware has tcp src port rule installed -->
>
>   #tc qdisc del dev eth4 parent ffff:
>
> <-- hardware cleaned up -->
>

All looks cool but I am just worried about the lack of intent that
something needs to go to hw vs sw. Other worry:
What happens when things fail to install in hw?
As it stands right now your assumption is all default rules go to h/w.
And failure to install is not handled.
I know Dave wants to push this in so a followup sets of patches to
address this is fine by me. Otherwise if it is not too much work, please
address this.

cheers,
jamal