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

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Message-ID: <CA+sq2Cd51mYHbSsjUKL23MbLkHr=oKYWvuubspg37AEo2fE8vg@mail.gmail.com>
Date:   Sun, 22 Oct 2023 11:23:22 +0530
From:   Sunil Kovvuri <sunil.kovvuri@...il.com>
To:     "Nambiar, Amritha" <amritha.nambiar@...el.com>
Cc:     Hariprasad Kelam <hkelam@...vell.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

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.
> >
>
> 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://lore.kernel.org/netdev/20220921132929.3f4ca04d@kernel.org/
>
> 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.