[Cerowrt-devel] SQM and PPPoE, more questions than answers...

[Sebastian Moeller]

Hi Dave,

On Oct 15, 2014, at 19:28 , Dave Taht <dave.taht at gmail.com> wrote:

> hmm. The pppoe LLC packets are sparse and should already be optimized
> by fq_codel, but I guess I'll go look at the construction of those
> headers. Perhaps they need to be decoded better in the flow_dissector
> code?

	So when shaping on pppoe-ge00 one does not see the LLC packets at all (tested with tcpdump -i pppoe-ge00), since they are added after the shaping. (tcpdump -i ge00 does see th dllc packets) I have no idea whether pppd issues these with higher priority or not.


> 
> I also made some comments re the recent openwrt pull request.
> 
> https://github.com/dtaht/ceropackages-3.10/commit/b9e3bafdabb3c5aa47f8f63eae2ecfe34c361855
> 
> SQM need not require the advanced qdiscs package, if it checks for
> availability of the other qdiscs,

	Well, but how to do this, I know of no safe way, except testing availability of modules for a known set of qdiscs, but what if the qdiscs are built into a monolithic kernel? Does anyone here have a good idea of how to detect all qdiscs available to the running kernel?

Best Regards
	Sebastian

> and even then nobody's proposed
> putting the new nfq_codel stuff into openwrt - as it's still rather
> inadaquately tested, and it's my hope that cake simplifies matters
> significantly when it's baked. I already have patches for sqm for it,
> but it's just not baked enough...
> 
> Also I think exploring policing at higher ingres bandwidths is warrented…
> 
> On Wed, Oct 15, 2014 at 6:39 AM, Sebastian Moeller <moeller0 at gmx.de> wrote:
>> Hi Edwin,
>> 
>> 
>> On Oct 15, 2014, at 14:02 , Török Edwin <edwin+ml-cerowrt at etorok.net> wrote:
>> 
>>> On 10/15/2014 03:03 AM, Sebastian Moeller wrote:
>>>>     I guess it is back to the drawing board to figure out how to speed up the classification… and then revisit the PPPoE question again…
>>> 
>>> FWIW I had to add this to /etc/config/network (done via luci actually):
>>> option keepalive '500 30'
>>> 
>>> Otherwise it uses these default values from /etc/ppp/options, and then I hit: https://dev.openwrt.org/ticket/7793:
>>> lcp-echo-failure 5
>>> lcp-echo-interval 1
>>> 
>>> The symptomps are that if I start a large download after half a minute or so pppd complains that it didn't receive reply to 5 LCP echo packets and disconnects/reconnects.
>> 
>>        I have not yet seen these in the logs, but I will keep my eyes open.
>> 
>>> Sounds like the LCP echo/reply packets should get prioritized, but I don't know if it is my router that is dropping them or my ISP.
>> 
>>        I think that is something we should be able to teach SQM (as long as the shaper is running on the lower ethernet interface and not the pppoe interface).
>> 
>>> 
>>> When you tested PPPoE did you notice pppd dropping the connection and restarting, cause that would affect the timings for sure…
>> 
>>        Nope, what I see is simply more variance in bandwidth and latency numbers and a less step slope on a right shifted ICMP CDF… I assume that the disconnect reconnects should show up as periods without any data transfer….
>> 
>> Mmmh, I will try to put the PPP service packets into the highest priority class and see whether that changes things, as well as testing your PPP options.
>> 
>> Thanks for your help
>> 
>>        Sebastian
>> 
>>> 
>>> Best regards,
>>> --Edwin
>>> 
>>> 
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>> 
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> 
> 
> 
> -- 
> Dave Täht
> 
> thttp://www.bufferbloat.net/projects/bloat/wiki/Upcoming_Talks