netdev - Re: PPPoE performance regression

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Date:	Wed, 13 Jun 2012 13:21:22 -0400
From:	Benjamin LaHaise <bcrl@...ck.org>
To:	David Woodhouse <dwmw2@...radead.org>
Cc:	Nathan Williams <nathan@...verse.com.au>,
	Karl Hiramoto <karl@...amoto.org>,
	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	Paul Mackerras <paulus@...ba.org>,
	John Crispin <blogic@...nwrt.org>
Subject: Re: PPPoE performance regression

On Wed, Jun 13, 2012 at 05:53:03PM +0100, David Woodhouse wrote:
> I'm looking at the class of device on which OpenWRT runs. Linux is *on*
> the router with the ADSL port, not connected to it via Ethernet.

Ah, yes, that's a worthwhile pursuit.

> And even if it *were* rare... this is the case that *should* work best,
> where we have complete control of the hardware. There's no excuse for
> the behaviour that we currently see with PPPoE on BR2684.

*nod*

> I think that's largely true of BQL in general, isn't it? That's OK; it's
> a config option. I suspect if I make this accounting of PPPoE / L2TP
> packets conditional on BQL (or perhaps on a separate config option
> PPP_BQL) that ought to address your concern about the cases where you
> don't need it?

That would help.

On the whole question of PPPoE over intermediate ethernet links to ADSL 
modems, I think it would be possible to limit latency by implementing a 
sliding window clocked using LCP ECHO requests.  Does this sound worthwhile 
implementing?  What sort of queue depths are you looking at for the ATM 
devices you're working on?

		-ben
-- 
"Thought is the essence of where you are now."
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