linux-kernel - Re: [Patch] fix packet loss and massive ping spikes with PPP multi-link

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Date:	Wed, 02 Jun 2010 15:55:30 +0100
From:	Ben McKeegan <ben@...servers.co.uk>
To:	Paul Mackerras <paulus@...ba.org>
CC:	netdev@...r.kernel.org, linux-ppp@...r.kernel.org,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	"Alexander E. Patrakov" <patrakov@...il.com>,
	Richard Hartmann <richih.mailinglist@...il.com>,
	linux-kernel@...r.kernel.org, gabriele.paoloni@...el.com
Subject: Re: [Patch] fix packet loss and massive ping spikes with PPP multi-link

Ben McKeegan wrote:
> Paul Mackerras wrote:
> 
>>> I needed to do something similar a while back and I took a very
>>> different approach, which I think is more flexible.   Rather than
>>> implement a new round-robin scheduler I simply introduced a target
>>> minimum fragment size into the fragment size calculation, as a per
>>> bundle parameter that can be configured via a new ioctl.  This
>>> modifies the algorithm so that it tries to limit the number of
>>> fragments such that each fragment is at least the minimum size.  If
>>> the minimum size is greater than the packet size it will not be
>>> fragmented all but will instead just get sent down the next
>>> available channel.
>>>
>>> A pppd plugin generates the ioctl call allowing this to be tweaked
>>> per connection.  It is more flexible in that you can still have the
>>> larger packets fragmented if you wish.
>>
>> I like this a lot better than the other proposed patch.  It adds less
>> code because it uses the fact that ppp_mp_explode() already has a
>> round-robin capability using the ppp->nxchan field, plus it provides a
>> way to control it per bundle via pppd.
>>
>> If you fix up the indentation issues (2-space indent in some of the
>> added code -- if you're using emacs, set c-basic-offset to 8), I'll
>> ack it and hopefully DaveM will pick it up.
> 
> Okay, I'll fix it up when I'm back at work Tuesday and submit (today is 
> a UK public holiday) and also dig out and fix up the userspace code to 
> go with it.

Still working on this, updating the patch wasn't as trivial as I thought 
as it clashed with Gabriele Paoloni's ppp_mp_explode redesign.  However, 
while looking at this code I believe I have found a bug which might have 
been contributing to the poor performance the OP was experiencing.   For 
the case where channel speeds are unknown and there are more than 2 
channels it would miscalculate the fragment sizes so they are not 
balanced on the channels.

Patch for the bug to follow immediately.

Regards,
Ben.
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