[c-nsp] packet processing delay & LLQ

[Oliver Boehmer (oboehmer)]

Dmitry Volkov <mailto:dmitry.volkov at rogers.com> wrote on Thursday, March
17, 2005 5:15 AM:

> Volodymyr,
> 
> try to change "tx-ring-limit 4"
> 
> Oliver, since You are from Cisco, would You please let us know
> whether this below is valid for serial interfaces as well ? : 

In general, tx-ring-limit tuning is not needed (and not recommended when
using CBWFQ/LLQ). When Queuing is enabled on a E1/T1 interface, tx-limit
is set to 2, which in effect creates the backpressure we need to perform
fancy queuing on the pkt..

> I don't see any reason for FIFO queue when CBWFQ is enabled

Well, at the end this is a serial interfaces where packets are sent in
order. This (very short) FIFO-Queue is way deep in the driver right
before the pkts are pushed onto the link, any fancy queuing happens
before the pkts are handed over to the driver..

	oli

> 
>> -----Original Message-----
>> From: cisco-nsp-bounces at puck.nether.net
>> [mailto:cisco-nsp-bounces at puck.nether.net]On Behalf Of Oliver
>> Boehmer (oboehmer)
>> Sent: Tuesday, March 15, 2005 11:21 AM
>> To: Volodymyr Yakovenko; cisco-nsp at puck.nether.net
>> Subject: RE: [c-nsp] packet processing delay & LLQ
>> 
>> 
>> 
>>> 
>>>  I need some advice in LLQ tuning for delay-critical traffic.
>>> 
>>>  As far as I know the right way to provide minimal delay for certain
>>>  type of traffic is to put it into priority queue.
>>> 
>>>  To test it out I am using 2M Serial connected 2610 (Serial0/0) with
>>>  the following LLQ configuration:
>>> 
>>> ip access-list ext NOC
>>>  permit ip any host 172.20.2.20
>>>  permit ip host 172.20.2.20 any
>>> class-map match-any IS-NOC
>>>   match access-group name NOC
>>> policy-map E2
>>>   class IS-NOC
>>>    priority 512
>>>   class class-default
>>>    fair-queue
>>> int Serial0/0
>>>  service-policy output E2
>>> 
>>>  In clean channel case (no other traffic flowing on link) RTT (ping
>>>  to 172.20.2.20) over Serial is about 3ms. When I am saturating
>>>  link with class-default traffic RTT jumps to about 90-110ms and
>>>  remains almost stable. Priority queue works (class-default traffic
>>>  RTT is 200ms and more), but delay value is not applicable.
>> 
>> you have LLQ enabled on both ends of the connection? Where is the
>> 172.20.2.20 located? On the router itself? What is the CPU load of
>> the box when you saturate the link?
>> 
>> 	oli
>> 
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