On 11/9/21 8:24 PM, Numan Siddique wrote:
> On Fri, Nov 5, 2021 at 5:21 AM Dumitru Ceara <[email protected]> wrote:
>>
>> There are various costs (e.g., not being able to perform hardware
>> offload in some cases) when using check_pkt_larger() so the CMS
>> can now limit the impact by bypassing the packet length checks for
>> specific types of traffic (e.g., TCP).
>>
>> Reported-at: https://bugzilla.redhat.com/show_bug.cgi?id=2011779
>> Signed-off-by: Dumitru Ceara <[email protected]>
>
>
> Hi Dumitru,
>
Hi Numan,
Thanks for reviewing this!
> Thanks for the patch. Instead of adding a bypass option, how about adding
> the option to check for the extra matches ?
We could do that too, even if it's just for making it more natural to
configure.
>
> i.e new option can be - gateway_mtu_match. And ovn-northd would append
> this match to the existing logical flows with the action - check_pkt_larger ?
That wouldn't work directly. That's because we already append
check_pkt_larger() to flows that perform other actions.
Let's assume we start with gateway_mtu not configured, then we'd have
(at least) the following flows:
- table=rtr_in_admission,prio=50, eth.mcast && inport == <rtr-port>,
actions='REG_INPORT_ETH_ADDR = <rtr-port>.eth, next;'
- table=rtr_in_admission,prio=50, eth.dst == <rtr-port> && inport ==
<rtr-port> && is_chassis_resident(<rtr-port>),
actions='REG_INPORT_ETH_ADDR = <rtr-port>.eth, next;'
If we now configure gateway_mtu=1400 these flows get changed to:
- table=rtr_in_admission,prio=50, eth.mcast && inport == <rtr-port>,
actions='REG_INPORT_ETH_ADDR = <rtr-port>.eth;
reg9[1]=check_pkt_larger(1428); next;'
- table=rtr_in_admission,prio=50, eth.dst == <rtr-port> && inport ==
<rtr-port> && is_chassis_resident(<rtr-port>),
actions='REG_INPORT_ETH_ADDR = <rtr-port>.eth;
reg9[1]=check_pkt_larger(1428); next;'
Just adding an extra gateway_mtu_match to the matches of the two flows
above would be wrong as we would not be performing the other actions
("REG_INPORT_ETH_ADDR = <rtr-port>; next;") for all traffic that doesn't
need check_pkt_larger.
>
> This would not increase the number of lflows ? It's possible that I may have
> missed a few details/scenarios. What do you think?
Due to the reasons above, this other approach you're suggesting would
unfortunately also have to increase the number of flows. However, we're
not talking about a huge increase because we currently have at most 3
flows per logical router port that has gateway_mtu enabled. I don't
expect the number of such ports to be huge.
>
> Otherwise the patch LGTM.
>
If you think it makes more sense to configure "gateway_mtu_match"
instead of "gateway_mtu_bypass", I'm ok with that and I can send a v3
but the implementation would be very similar to the one in v2.
Thanks,
Dumitru
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