linux-kernel - Re: [net-next Patch v2 4/5] octeontx2-pf: Add devlink support to configure TL1 RR

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Date:   Tue, 24 Jan 2023 01:01:21 +0200
From:   Maxim Mikityanskiy <maxtram95@...il.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Hariprasad Kelam <hkelam@...vell.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        Sunil Kovvuri Goutham <sgoutham@...vell.com>,
        Linu Cherian <lcherian@...vell.com>,
        Geethasowjanya Akula <gakula@...vell.com>,
        Jerin Jacob Kollanukkaran <jerinj@...vell.com>,
        Subbaraya Sundeep Bhatta <sbhatta@...vell.com>,
        "jhs@...atatu.com" <jhs@...atatu.com>,
        "xiyou.wangcong@...il.com" <xiyou.wangcong@...il.com>,
        "jiri@...nulli.us" <jiri@...nulli.us>,
        "saeedm@...dia.com" <saeedm@...dia.com>,
        "richardcochran@...il.com" <richardcochran@...il.com>,
        "tariqt@...dia.com" <tariqt@...dia.com>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "hariprasad.netdev@...il.com" <hariprasad.netdev@...il.com>,
        Naveen Mamindlapalli <naveenm@...vell.com>
Subject: Re: [net-next Patch v2 4/5] octeontx2-pf: Add devlink support to
 configure TL1 RR_PRIO

On Mon, Jan 23, 2023 at 02:45:48PM -0800, Jakub Kicinski wrote:
> On Mon, 23 Jan 2023 22:05:58 +0200 Maxim Mikityanskiy wrote:
> > OK, I seem to get it now, thanks for the explanation!
> > 
> > How do you set the priority for HTB, though? You mentioned this command
> > to set priority of unclassified traffic:
> > 
> > devlink -p dev param set pci/0002:04:00.0 name tl1_rr_prio value 6 \
> > cmode runtime
> > 
> > But what is the command to change priority for HTB?
> > 
> > What bothers me about using devlink to configure HTB priority is:
> > 
> > 1. Software HTB implementation doesn't have this functionality, and it
> > always prioritizes unclassified traffic. As far as I understand, the
> > rule for tc stuff is that all features must have a reference
> > implementation in software.
> > 
> > 2. Adding a flag (prefer unclassified vs prefer classified) to HTB
> > itself may be not straightforward, because your devlink command has a
> > second purpose of setting priorities between PFs/VFs, and it may
> > conflict with the HTB flag.
> 
> If there is a two-stage hierarchy the lower level should be controlled
> by devlink-rate, no?

>From the last picture by Hariprasad, I understood that the user sets all
priorities (for unclassified traffic per PF and VF, and for HTB traffic)
on the same TL2 level, i.e. it's not two-stage. (Maybe I got it all
wrong again?)

I asked about the command to change the HTB priority, cause the
parameters aren't easily guessed, but I assume it's also devlink (i.e.
driver-specific).

If there were two levels (the upper level chooses who goes first: HTB or
unclassified, and the lower level sets priorities per PF and VF for
unclassified traffic), that would be more straightforward to solve: the
upper level should be controlled by a new HTB parameter, and the lower
level is device-specific, thus it goes to devlink.