netdev - Re: [PATCH net-next 0/5] mlxsw: Add support for RED qevent "mark"

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Message-ID: <20210123115527.58d0f04c@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Sat, 23 Jan 2021 11:55:27 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Ido Schimmel <idosch@...sch.org>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, petrm@...dia.com,
        jiri@...dia.com, amcohen@...dia.com, mlxsw@...dia.com,
        Ido Schimmel <idosch@...dia.com>
Subject: Re: [PATCH net-next 0/5] mlxsw: Add support for RED qevent "mark"

On Sat, 23 Jan 2021 17:28:02 +0200 Ido Schimmel wrote:
> > Thanks for the explanation. I feel more and more convinced now that
> > we should have TC_ACT_TRAP_MIRROR and the devlink trap should only 
> > be on/off :S Current model of "if ACT_TRAP consult devlink for trap
> > configuration" is impossible to model in SW since it doesn't have a
> > equivalent of devlink traps. Or we need that equivalent..  
> 
> Wait, the current model is not "if ACT_TRAP consult devlink for trap
> configuration". 'ecn_mark' action is always 'trap' ('mirror' in v2) and
> can't be changed. Such packets can always be sent to the CPU, but the
> decision of whether to send them or not is based on the presence of tc
> filters attached to RED's 'mark' qevent with TC_ACT_TRAP
> (TC_ACT_TRAP_MIRROR in v2).

I see, missed that, but I think my point conceptually stands, right?
Part of forwarding behavior was (in v1) only expressed in control 
plane (devlink) not dataplane (tc).
 
> I believe that with the proposed changes in v2 it should be perfectly
> clear that ECN marked packets are forwarded in hardware and a copy is
> sent to the CPU.

Yup, sounds good.