netdev - Re: [Intel-wired-lan] Question on ixgbe flow director

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Date:   Wed, 8 Mar 2017 07:39:49 -0800
From:   Alexander Duyck <alexander.duyck@...il.com>
To:     tndave <tushar.n.dave@...cle.com>
Cc:     intel-wired-lan <intel-wired-lan@...ts.osuosl.org>,
        netdev <netdev@...r.kernel.org>,
        Sowmini Varadhan <sowmini.varadhan@...cle.com>
Subject: Re: [Intel-wired-lan] Question on ixgbe flow director

On Tue, Mar 7, 2017 at 3:43 PM, tndave <tushar.n.dave@...cle.com> wrote:
> Hi,
>
> I have few questions regarding ixgbe flow director.
> As per my understanding flow director in ixgbe can work in 2 exclusive ways,
> a. Using ATR filters - where flow director is setup in HW by driver
> identifying transmit traffic. And based on that, receive traffic of the
> same flow get assigned/directed to same queue.

So ATR for ixgbe uses the Flow Director signature filters.  Basically
the signature filters are purely hash based filters.  The easiest way
to think of it is it is essentially a beefed up version of RSS.

> b. Perfect filter, where user can manually program flow director using
> ethtool so that receive packets gets directed to specified rx queue
> (depending on on how ethtool flow-type and action etc,.); But with
> perfect filters there is no intelligence involved alike ATR has on
> identifying transit, right?

You are right.  The perfect match filters are the ones we configure
via ethtool.  You are correct in that ATR logic is not involved so
there is no matching up an Rx flow to a Tx flow.

> Few question regarding ixgbe ATR,
> 1. does ATR works in case if protocol is UDP? (Based on the current
> ixgbe_atr() it only supports TCP)

It could, but the software for doing ATR flow identification,
ixgbe_atr(), only works on TCP.  The reasoning behind it is that Flow
Director doesn't filter fragmented frames and UDP can be fragmented.

> 2. Does ATR flow director can be programmed using ethtool?
> (As per my understanding only perfect filter can be programmed from
> ethtool, is that so?)

You can enable/disable the ATR filters via the NTUPLE feaure flag.
Basically it toggles between ATR mode, and NTUPLE mode.  In NTUPLE
mode the perfect filters are enabled and can be configured via
ethtool.

> Thanks in advance,
> -Tushar

Hope that helps.

- Alex