Message-ID: <6661bb98-6cec-a82f-e234-391facda9cd3@oracle.com>
Date:   Wed, 8 Mar 2017 14:56:50 -0800
From:   tndave <tushar.n.dave@...cle.com>
To:     Alexander Duyck <alexander.duyck@...il.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 03/08/2017 01:03 PM, Alexander Duyck wrote:
> On Wed, Mar 8, 2017 at 11:30 AM, tndave <tushar.n.dave@...cle.com> wrote:
>>
>>
>> On 03/08/2017 07:39 AM, Alexander Duyck wrote:
>>>
>>> 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.
>>
>> Alex,
>>
>> Thanks for the info.
>>>
>>>
>>>> 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.
>>
>> So we could just add code in ixgbe_atr() for non-fragmented udp packets!
>> However question is if it is going to work w.r.t ATR? TCP is connected
>> stream vs udp is stateless and single udp socket can talk to multiple
>> endpoints.
>
> Right so the Tx based approach for UDP also probably won't work
> because there isn't a symmetric set of endpoints used for most UDP
> flows.  For example with TCP you have a fixed set of source and
> destination ports that you can swap and get the opposite direction.
> The same isn't true for UDP.  You can end up with UDP using a random
> source port and sending to the same fixed destination port on both
> ends.
>
> You might look at the hardware RPS offload that some of the other
> drivers out there support that allow for hardware accelerated RFS
> offload.  Something like that might work for your needs if you are
> needing to route UDP.
Okay. Thanks Alex.

-Tushar
>
>>>
>>>> 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.
>>
>> Got it.
>>
>> Thanks.
>>
>> -Tushar
>>
>>>
>>>> Thanks in advance, -Tushar
>>>
>>>
>>> Hope that helps.
>>>
>>> - Alex
>>>
>>
>

Powered by blists - more mailing lists