Date:   Wed, 16 Aug 2017 20:32:11 -0700
From:   Ben Greear <greearb@...delatech.com>
To:     Dan Williams <dcbw@...hat.com>, David Miller <davem@...emloft.net>
Cc:     james@...ealm.net, futur.andy@...glemail.com, kvalo@...eaurora.org,
        arend.vanspriel@...adcom.com, maheshb@...gle.com,
        andy@...yhouse.net, netdev@...r.kernel.org,
        linux-wireless@...r.kernel.org
Subject: Re: Regression: Bug 196547 - Since 4.12 - bonding module not working
 with wireless drivers

On 08/16/2017 08:18 PM, Dan Williams wrote:
> On Wed, 2017-08-16 at 19:36 -0700, Ben Greear wrote:
>> On 08/16/2017 07:11 PM, Dan Williams wrote:
>>> On Wed, 2017-08-16 at 14:31 -0700, David Miller wrote:
>>>> From: Dan Williams <dcbw@...hat.com>
>>>> Date: Wed, 16 Aug 2017 16:22:41 -0500
>>>>
>>>>> My biggest suggestion is that perhaps bonding should grow
>>>>
>>>> hysteresis
>>>>> for link speeds. Since WiFi can change speed every packet, you
>>>>
>>>> probably
>>>>> don't want the bond characteristics changing every couple
>>>>> seconds
>>>>
>>>> just
>>>>> in case your WiFi link is jumping around.  Ethernet won't
>>>>> bounce
>>>>
>>>> around
>>>>> that much, so the hysteresis would have no effect there.  Or,
>>>>> if
>>>>
>>>> people
>>>>> are concerned about response time to speed changes on ethernet
>>>>
>>>> (where
>>>>> you probably do want an instant switch-over) some new flag to
>>>>
>>>> indicate
>>>>> that certain devices don't have stable speeds over time.
>>>>
>>>> Or just report the average of the range the wireless link can
>>>> hit,
>>>> and
>>>> be done with it.
>>>>
>>>> I think you guys are overcomplicating things.
>>>
>>> That range can be from 1 to > 800Mb/s.  No, it won't usually be all
>>> over that range, but it won't be uncommon to fluctuate by hundreds
>>> of
>>> Mb/s.  I'm not sure a simple average is really the answer
>>> here.  Even
>>> doing that would require new knobs to ethtool, since the rate
>>> depends
>>> heavily on card capabilities and also what AP you're connected to
>>> *at
>>> that moment*.  If you roam to another AP, then the max speed can
>>> certainly change.
>>>
>>> You'll probably say "aim for the 75% case" or something like that,
>>> which is fine, but then you're depending on your 75% case to be (a)
>>> single AP, (b) never move (eg, only bond wifi + ethernet), (c)
>>> little
>>> radio interference.  I'm not sure I'd buy that.  If I've put words
>>> in
>>> your mouth, forgive me.
>>
>> If you keep ethtool API simple and just return the last (rx-rate +
>> tx-rate) / 2, or the rate averaged
>> over the last 100 frames or 10 seconds, then the caller can do longer
>> term averaging
>> as it sees fit.  Probably no need for lots of averaging complexity in
>> the kernel.
>
> Yeah, that works too, but I was thinking it was better to present the
> actual data through ethtool so that things other than bonding could use
> it, and since bonding is the thing that actually cares about the
> fluctuation, make it do the more extensive processing.

What do you mean by 'actual data'?  If you want to know the most accurate
transmit/rx rate info, then you need to pay attention to each and every frame's tx/rx rate, as
well as it's ampdu/amsdu, retries, etc.  It is virtually impossible.

So, you will have to settle for something less...  I suggest something simple
to calculate, similar to existing values that are available via debugfs and/or
'iw dev foo station dump', etc.  Let higher layers manipulate the raw data
as they see fit (they can query ethtool as often as they like).

Thanks,
Ben


-- 
Ben Greear <greearb@...delatech.com>
Candela Technologies Inc  http://www.candelatech.com

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