netdev - Re: Regression: Bug 196547 - Since 4.12 - bonding module not working with wireless drivers

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Date:   Wed, 16 Aug 2017 22:18:14 -0500
From:   Dan Williams <dcbw@...hat.com>
To:     Ben Greear <greearb@...delatech.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 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.

Dan


> rate-ctrl for wifi basically doesn't happen until you transmit or
> receive a
> fairly steady stream, so it will fluctuate a lot.