netdev - Re: Query on new ethtool RSS hashing options

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Message-ID: <CA+sq2CfAsyFHEj=w3=ewTKk-qbF60FcCQNtk9e7_1wxf=tB7QA@mail.gmail.com>
Date:   Sat, 6 Mar 2021 18:04:14 +0530
From:   Sunil Kovvuri <sunil.kovvuri@...il.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Jakub Kicinski <kuba@...nel.org>,
        Linux Netdev List <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        George Cherian <gcherian@...vell.com>,
        Subbaraya Sundeep <sbhatta@...vell.com>,
        Sunil Goutham <sgoutham@...vell.com>,
        Vladimir Oltean <vladimir.oltean@....com>
Subject: Re: Query on new ethtool RSS hashing options

On Sat, Mar 6, 2021 at 5:47 AM Andrew Lunn <andrew@...n.ch> wrote:
>
> On Fri, Mar 05, 2021 at 03:07:02PM -0800, Jakub Kicinski wrote:
> > On Fri, 5 Mar 2021 16:15:51 +0530 Sunil Kovvuri wrote:
> > > Hi,
> > >
> > > We have a requirement where in we want RSS hashing to be done on packet fields
> > > which are not currently supported by the ethtool.
> > >
> > > Current options:
> > > ehtool -n <dev> rx-flow-hash
> > > tcp4|udp4|ah4|esp4|sctp4|tcp6|udp6|ah6|esp6|sctp6 m|v|t|s|d|f|n|r
> > >
> > > Specifically our requirement is to calculate hash with DSA tag (which
> > > is inserted by switch) plus the TCP/UDP 4-tuple as input.
> >
> > Can you share the format of the DSA tag? Is there a driver for it
> > upstream? Do we need to represent it in union ethtool_flow_union?
>
> Sorry, i missed the original question, there was no hint in the
> subject line that DSA was involved.
>
> Why do you want to include DSA tag in the hash? What normally happens
> with DSA tag drivers is we detect the frame has been received from a
> switch, and modify where the core flow dissect code looks in the frame
> to skip over the DSA header and parse the IP header etc as normal.

I understand your point.
The requirement to add DSA tag into RSS hashing is coming from one of
our customer.

>
> Take a look at net/core/flow_dissect.c:__skb_flow_dissect()
>
> This fits with the core ideas of the network stack and offloads. Hide
> the fact an offload is being used, it should just look like a normal
> interface.
>
>         Andrew

Yes, the pkt will look like a normal packet itself.
In our case HW strips the DSA tag from the packet and forwards it to a VF.

Thanks,
Sunil.