linux-kernel - Re: [net-next] net: sched: extend flow action with RSS

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Message-ID: <PH0PR18MB44745BC53FFEAD9F8ECAFED6DED8A@PH0PR18MB4474.namprd18.prod.outlook.com>
Date:   Mon, 23 Oct 2023 04:04:06 +0000
From:   Hariprasad Kelam <hkelam@...vell.com>
To:     Dave Taht <dave.taht@...il.com>,
        Sunil Kovvuri <sunil.kovvuri@...il.com>
CC:     "Nambiar, Amritha" <amritha.nambiar@...el.com>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        "sridhar.samudrala@...el.com" <sridhar.samudrala@...el.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kuba@...nel.org" <kuba@...nel.org>,
        Sunil Kovvuri Goutham <sgoutham@...vell.com>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "xiyou.wangcong@...il.com" <xiyou.wangcong@...il.com>,
        "jiri@...nulli.us" <jiri@...nulli.us>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [net-next] net: sched: extend flow action with RSS



> -----Original Message-----
> From: Dave Taht <dave.taht@...il.com>
> ----------------------------------------------------------------------
> On Sat, Oct 21, 2023 at 10:53 PM Sunil Kovvuri <sunil.kovvuri@...il.com>
> wrote:
> >
> > On Sat, Oct 21, 2023 at 1:43 AM Nambiar, Amritha
> > <amritha.nambiar@...el.com> wrote:
> > >
> > > >> On Fri, Oct 20, 2023 at 2:12 AM Hariprasad Kelam
> > > >> <hkelam@...vell.com>
> > > >> wrote:
> > > >>>
> > > >>> This patch extends current flow action with RSS, such that the
> > > >>> user can install flower offloads with action RSS followed by a group
> id.
> > > >>> Since this is done in hardware skip_sw flag is enforced.
> > > >>
> > > >> Our typical rule for TC is we need s/w equivalence for offloads.
> > > >> How would this work in absence of offload?
> > > >>
> > > > [Hari]
> > > > Our typical rule for TC is we need s/w equivalence for offloads. How
> would this work in absence of offload?
> > > >
> > > > This patch we added as an extension to receive queue selection in
> hardware.
> > > > This patch "act_skbedit: skbedit queue mapping for receive queue"
> > > > enabled receive queue selection in hardware and skip_sw is enforced.
> > > >
> > > > Adding stakeholders of this patch, to get their opinion.
> > > > sridhar.samudrala@...el.com  amritha.nambiar@...el.com
> > > >
> > > > incase of RSS, hardware makes decisions about incoming packets
> before they are even received in the queue.
> 
> Is there any way to do a LPM to queue match on inbound?
> 
AFAIK, LPM (longest prefix match) is used to make routing decisions by comparing the destination ip address bit-by-bit with prefixes in the routing table.
Where on a typice UDP/TCP packet, RSS considers Source IP/Destination IP and Sport and Dport these fields to make decision on the queue mapping.



> > > >
> > >
> > > The skip_sw for skbedit receive queue action was enforced as the
> > > only other alternative was a new hw-only action, or changing the
> > > action mirred. See discussion at
> > > https://urldefense.proofpoint.com/v2/url?u=https-3A__lore.kernel.org
> > > _netdev_20220921132929.3f4ca04d-
> 40kernel.org_&d=DwIFaQ&c=nKjWec2b6R0
> > > mOyPaz7xtfQ&r=2bd4kP44ECYFgf-
> KoNSJWqEipEtpxXnNBKy0vyoJJ8A&m=_GDltrUw
> > > pNUkk5hvYOtlzFeW-rAeZy4_1bSWUdGVen-
> sJDjMWkmLw7pVfDH7OHBX&s=SGwkF4_m8
> > > 5hkScL8rNnbVPvDwEnNalysi6x6ual5NHY&e=
> > >
> > > Few questions WRT this patch:
> > > How are the rss groups created? ethtool rss contexts? Any reason to
> > > use TC to direct to rss contexts over using ethtool context ids?
> > >
> >
> > Yes, RSS groups are created using ethtool.
> > Ethtool ntuple is very limited in expressing flow rules and since the
> > general direction is to use 'TC', we are attempting to add RSS action
> > to 'TC'.
> >
> >
> > > IIUC, skbedit is meant to only edit skb metadata such as mark,
> > > packet type, queue mapping, priority etc. Even if this is a HW only
> > > action and has no use in the stack, would skbedit be the right fit here?
> > >
> >
> > The thought was to keep related actions like RQ, RSS group etc under
> > one action ie skbedit.
> > If that's not the right place we can add a separate action.
> >
> > Thanks,
> > Sunil.
> >
> 
> 
> --
> Oct 30: https://urldefense.proofpoint.com/v2/url?u=https-
> 3A__netdevconf.info_0x17_news_the-2Dmaestro-2Dand-2Dthe-2Dmusic-
> 2Dbof.html&d=DwIFaQ&c=nKjWec2b6R0mOyPaz7xtfQ&r=2bd4kP44ECYFgf-
> KoNSJWqEipEtpxXnNBKy0vyoJJ8A&m=_GDltrUwpNUkk5hvYOtlzFeW-
> rAeZy4_1bSWUdGVen-
> sJDjMWkmLw7pVfDH7OHBX&s=gKGp2Lqrx7O6ZAfoWGSQeb__T6PYk8SzKHSf
> SxtoNLU&e=
> Dave Täht CSO, LibreQos